Fibrous sheets coated or impregnated with biodegradable polymers or polymers blends

ABSTRACT

Fibrous sheets are coated or impregnated with a biodegradable composition to render the sheets more resistant to penetration by liquids. Biodegradable polymer blends suitable for use in coating or impregnating a fibrous sheet can be manufactured from at least one “hard” biodegradable polymer and at least one “soft” biodegradable polymer. “Hard” biopolymers typically have a glass transition temperature of at least about 10° C. “Soft” biodegradable polymers typically have a glass transition temperature less than about 0° C. Another useful biodegradable polymer composition includes one or more biodegradable polymers and sufficient inorganic filler so as to render the treated sheet microwaveable. The biodegradable polymer compositions are especially well-suited for coating or impregnating paper sheets, e.g., 12-15 lb/3000 ft 2  tissue paper to yield food wraps. Food wraps will typically be manufactured to have good “dead-fold” properties so as to remain in a wrapped position and not spring back to an “unwrapped” form.

BACKGROUND OF THE INVENTION

[0001] 1. The Field of the Invention

[0002] The present invention relates generally to biodegradable polymersor polymer blends and sheets manufactured therefrom. More particularly,the present invention relates to fibrous sheets that are coated orimpregnated with biodegradable polymers or blends that render the sheetsmore resistant to liquids. The resulting sheets are suitable for anumber of applications, such as disposable wraps, bags, pouches or otherpackaging materials.

[0003] 2. The Relevant Technology

[0004] As affluence grows, so does the ability to purchase andaccumulate more things. Never before in the history of the world hasthere been such a large number of people with such tremendous buyingpower. The ability to purchase relatively inexpensive goods, such asbooks, tools, toys and food, is a luxury enjoyed by virtually all levelsof society, even those considered to be at the poorer end of thespectrum. Because a large percentage of what is purchased isprepackaged, there has been a tremendous increase in the amount ofdisposable packaging materials that are routinely discarded into theenvironment as solid waste. Thus, as society becomes more affluent, itgenerates more disposable trash.

[0005] Some packaging materials are only intended for a single use, suchas boxes, cartons, pouches, bags and wraps used to package itemspurchased from wholesale and retail outlets. Even the advent ofcomputers and “paperless” transactions has not stemmed the rising tideof packaging wastes. Indeed, the onset of “e-commerce” has spawned agreat mail-order fad, thus creating a whole new market of individuallypackaged and shipped items.

[0006] Moreover, the modern, fast-paced lifestyle has greatly disruptedtraditional eating routines in which people prepared their own meals andsat down as a family or group. Instead, people grab food on the run,thus creating ever-increasing amounts of fast-food packaging materialsthat are used once and then discarded. In view of the high volume ofdisposable packaging materials being generated, some countries,particularly those in Europe, have mandated either the recycling of fastfood generated wastes or the use of packaging materials which are“biodegradable” or “compostable”. Environmental activists commonlypressure companies that generate solid waste to find moreenvironmentally friendly alternatives. There is therefore anever-present need to develop biodegradable alternatives tononbiodegradable packaging materials.

[0007] Paper, paperboard and other fibrous sheets made from naturalcellulose-based fibers are biodegradable. However, fibrous sheets tendto be porous. As a result, they do not provide good barriers againstwater, oil or other liquids. When fibrous sheets are used inapplications where they will be exposed to liquids, they must generallybe treated with a liquid-resistant material, such as paraffin wax orplastic. By doing so, however, the fibrous sheets are no longerbiodegradable, but are as resistant to degradation as plastic orparaffin wax.

[0008] In view of the foregoing, it would be an advancement in the artto provide fibrous sheets that were resistant to liquids and that werebiodegradable. In addition or alternatively, it would be a furtheradvancement in the packaging art to provide improved fibrous sheets thatwere not only resistant to liquids, but still had good breathability andwater vapor transmission compared to conventional fibrous sheets treatedwith wax or plastic.

SUMMARY OF THE INVENTION

[0009] The invention encompasses fibrous sheets that are coated orimpregnated with biodegradable polymers or polymer blends in order toyield sheets that are more resistant to liquids (generally “treatedsheets” or “treated fibrous sheets”). The treated sheets can be used tomanufacture a wide variety of articles of manufacture, includingpackaging materials, such as wraps, bags, pouches, cartons, jugs, cups,plates, bowls, trays, platters, lids, straws, and the like.

[0010] Exemplary fibrous sheets that may be treated with biodegradablepolymers include, but are not limited to, tissue papers, paper sheets,felts, paperboard, wovens and nonwovens. In one aspect of the invention,fibrous sheets are coated or impregnated with a biodegradable polymerblend comprising at least one thermoplastic biodegradable polymer havingrelatively high stiffness and at least one thermoplastic biodegradablepolymer having relatively high flexibility. Thus, the present inventionprovides blends that possess or demonstrate surprising synergisticeffects that are particularly well-suited by use in treating fibroussheets.

[0011] For example, blends containing a relatively stiff BIOMAX polymer,a modified polyethylene terephthalate (PET) sold by DuPont, and arelatively soft or flexible polymer ECOFLEX, an aliphatic-aromaticcopolymer sold by BASF, and/or EASTAR BIO, an aliphatic-aromaticcopolymer sold by Eastman Chemical, have been shown to have strength andelongation properties which are superior to either biopolymer takenalone. Other stiff biopolymers include BAK, a polyesteramide sold byBayer, and polylactic acid (PLA).

[0012] BIOMAX is characterized as having a relatively high glasstransition temperature and is highly crystalline at room temperature.BIOMAX tends to be quite stiff or brittle when formed into films orsheets. It also has poor elongation or elasticity. ECOFLEX and EASTARBIO, on the other hand, are characterized as having relatively low glasstransition temperatures and are relatively amorphous or noncrystallineat room temperature, all of which contribute to the high softness,elasticity and high elongation. Even so, various blends of BIOMAX andECOFLEX and/or EASTAR BIO actually exhibit higher elongation thanECOFLEX by itself, as well as higher break stress compared to eitherBIOMAX or ECOFLEX by themselves.

[0013] Other polymer blends that can be used to treat fibrous sheetsinclude, but are not limited to, a blend of ECOFLEX, PLA andthermoplastic starch (TPS) and a blend of BAK (a polyesteramidemanufactured by Bayer Corporation) and TPS. In each case, blending abiopolymer having a relatively low glass transition temperature with abiopolymer having a relatively high glass transition temperature resultsin a polymer blend that exhibits the desired characteristics of eachpolymer by itself. In some cases, the blends exhibit better properties,while diminishing or minimizing the negative properties of eachbiopolymer by itself.

[0014] In general, biodegradable polymers that may be characterized asbeing relatively “stiff” or less flexible include polymers that have aglass transition temperature of at least about 10° C. Conversely,biodegradable polymers that may be characterized as being relatively“soft” include polymers that have a glass transition temperature lessthan about 0° C. “Stiff” biodegradable polymers preferably have a glasstransition temperature of at least about 15° C., more preferably atleast about 25° C., and most preferably at least about 35° C. “Soft”biodegradable polymers preferably have a glass transition temperature ofless than about −4° C., more preferably less than about −10° C., moreespecially preferably less than about −20° C., and most preferably lessthan about −30° C. In addition, “stiff” polymers tend to be morecrystalline, while “soft” polymers are generally less crystalline andmore amorphous, particularly at room temperature.

[0015] When a blend of soft and stiff biodegradable polymers is used tocoat or impregnate a fibrous sheet, the relatively stiff biodegradablepolymer may have a concentration in a range of about 20% to about 99% byweight of the blend of biodegradable polymers exclusive of the fibroussheet and any fillers. The stiff biodegradable polymer preferably has aconcentration of at least about 30% by weight of the polymer blend, morepreferably at least about 40% by weight of the polymer blend, moreespecially preferably greater than, but not including, 50% by weight ofthe polymer blend, and most preferably greater than about 55% by weightof the polymer blend.

[0016] When a blend of soft and stiff biodegradable polymers is used tocoat or impregnate a fibrous sheet, the relatively soft biodegradablepolymer may have a concentration in a range of about 1% to about 80% byweight of the blend of biodegradable polymers. The soft biodegradablepolymer preferably has a concentration up to about 70% by weight of thepolymer blend, more preferably up to about 60% by weight of the polymerblend, more especially preferably less than, but not including, 50% byweight of the polymer blend, and most preferably up to about 45% byweight of the polymer blend.

[0017] Biodegradable polymers used to treat fibrous sheets within thescope of the present invention include, but are not limited to,synthetic polyesters, semi-synthetic polyesters made by fermentation(e.g., PHB and PHBV), polyesteramides, polycarbonates, and polyesterurethanes. It is also within the scope of the invention to optionallyinclude a variety of natural polymers and their derivatives, such aspolymers comprising or derived from starch, cellulose, otherpolysaccharides and proteins. A single biodegradable polymer blendedwith an inorganic filler (e.g., silica or calcium carbonate) may also beused to treat a fibrous sheet in order to yield a treated sheet that ismore heat resistant.

[0018] It is within the scope of the invention to incorporate inorganicand organic fillers in order to decrease self-adhesion, lower the cost,and increase the modulus of elasticity (Young's modulus) ofbiodegradable polymers used to treat fibrous sheets as well as theresulting sheets. Examples of inorganic fillers include calciumcarbonate, titanium dioxide, silica, aluminum oxide, talc, mica, and thelike. Examples of organic fillers include wood flour, ground seeds,cellulose particles, polymeric particles, ungelatinized starch granules,and the like. In addition, plasticizers may be used to impart desiredsoftening and elongation properties.

[0019] In the case of fibrous sheets intended to be used as “wraps”,such as wraps used to enclose meats, other perishable food items, andespecially fast food items (e.g., sandwiches, burgers and dessertitems), it may be desirable to provide wraps having good “dead-fold”properties so that once folded, wrapped or otherwise manipulated into adesired orientation, such wraps will tend to substantially maintaintheir orientation so as to not spontaneously unfold or unwrap, as occurswith a large number of plastic sheets and films (e.g., polyethylene).Dead-fold is a measure of the ability of a sheet or film to retain acrease, crinkle or other bend. It is measured independently of selfcling, heat sealing, or the use of an adhesive to maintain a desiredorientation.

[0020] Whereas the fibrous sheets themselves may impart or inherentlypossess dead-fold properties, polymers and polymer blends used to treatfibrous sheets may be engineered so as to have a relatively high Young'smodulus, preferably at least about 100 MPa, more preferably at leastabout 150 MPa, and most preferably at least about 200 MPa. In general,increasing the concentration of the stiff biopolymer will tend toincrease the Young's modulus and the resulting dead-fold properties. Itshould be understood, however, that Young's modulus only looselycorrelates to dead-fold and does not, in every case, serve to define orpredict the dead-fold properties of a sheet or film formed from apolymer or polymer blend.

[0021] Including particulate fillers within the polymer or polymer blendused to coat or impregnate a fibrous sheet is another way to increasedead-fold of the resulting sheet. When used to increase dead-fold,particulate fillers are typically included in an amount of at leastabout 5% by weight of the polymer or polymer blend, preferably at leastabout 10% by weight, more preferably at least about 15% by weight, moreespecially preferably at least about 20% by weight, and most preferablyat least about 30% by weight of the polymer or polymer blend used totreat a fibrous sheet.

[0022] Yet another way to increase dead-fold is to increase the surfacearea, or “bulk hand feel”, of treated sheets according to the invention.This may be accomplished, for example, by disrupting the generallysmooth, planar nature of the treated sheet, e.g., by embossing,crimping, quilting or otherwise texturing the sheet so as to haveregularly spaced-apart or random hills and valleys rather than simplybeing a perfectly smooth, planar sheet. A treated sheet may be textured,for example, by passing the sheet through a pair of knurled or otherembossing-type rollers. Such texturing increases the ability of atreated sheet to take and maintain a fold, thus improving the dead-foldproperties of the sheet.

[0023] The surface area of a treated sheet may also be increased byincorporating particulate fillers within the polymer or polymer blendused to coat or impregnate the fibrous sheet in order form surfaceirregularities within the surface of the treated sheet. This may beaccomplished, for example, by incorporating filler particles, at least aportion of which, have a particle size diameter equal to or greater thanthe thickness of the polymer or polymer blend one or both sides of thetreated sheet.

[0024] When used to wrap foods, or whenever good dead-fold propertiesare desired, treated sheets according to the invention can be engineeredso as to have a dead-fold of at least about 50% (i.e., when creasedusing a standard dead-fold test, the sheets and films will maintain atleast about 50% of their original crease). Preferably, the treatedsheets will have a dead-fold of at least about 60%, more preferably atleast about 70%, more especially preferably at least about 80%, and mostespecially preferably at least about 90%. Treated fibrous sheetsaccording to the invention can have dead-fold approaching or equal to100% (i.e., when folded such sheets remain folded absent the applicationof an external force sufficient to reverse the fold). By way ofcomparison, sheets and films made from polyethylene (e.g., for use inmaking sandwich or garbage bags) typically have a dead-fold of 0%.

[0025] In some cases, it may be desirable for treated sheets accordingto the invention to “breath”. As set forth above, particulate fillers,both organic and inorganic, can be used to increase the modulus ofelasticity and/or dead-fold. Such fillers can also advantageously create“cavitation” whenever sheets or films used to coat or impregnate fibroussheets are stretched during processing. Cavitation occurs as thethermoplastic polymer fraction is pulled in either a monoaxial orbiaxial direction and the filler particles create a discontinuity in thefilm or sheet that increases in size during stretching. In essence, aportion of the stretched polymer pulls away from the filler particles,resulting in tiny cavities in the vicinity of the filler particles.This, in turn, results in greatly increased breathability and vaportransmission of the sheets and films. The ability of inorganic fillerparticles to create cavitation increases as the particle size diameterapproaches or exceeds the thickness of the polymer or polymer blend.

[0026] Another advantage of utilizing biodegradable polymers to treatfibrous sheets is that biopolymers are generally able to accept andretain print much more easily than conventional plastics or waxes usedto treat papers. Many plastics and waxes are highly hydrophobic and mustbe surface oxidized in order to provide a chemically receptive surfaceto which ink can adhere. Biodegradable polymers, on the other hand,typically include a significant fraction of oxygen-containing moieties,such as ester, amide and/or urethane groups, to which inks can morereadily adhere.

[0027] The treated sheets according to the invention may comprise singleor multiple layers as desired. The fibrous sheets can be impregnated orcoated on one or both sides, or any portion thereof. Multiple fibroussheets can be joined or sandwiched together with one or more layers ofbiodegradable polymers, and optionally one or more auxiliary sheets(e.g., metals foils). Fibrous sheets may be coated or impregnated byfilm blowing, co-extrusion, casting, and coating techniques known in theart. In one embodiment, a thermoplastic biodegradable composition isheated to a molten state and then spread over a fibrous sheet using adoctor blade. In another embodiment, the thermoplastic biodegradablecomposition is sprayed onto the fibrous sheet. Thermoplasticbiodegradable polymers used to treat fibrous sheets result in treatedsheets that can be heat sealed to join two ends together to form sacks,pockets, pouches, and the like. They can be laminated onto existingsheets or substrates.

[0028] Notwithstanding the advantages of using biodegradable polymersand polymer blends compared to polyethylene or other non-biodegradablepolymers, biodegradable polymers tend to have a much lower melt flowindex (MFI) compared to non-biodegradable polymers such as polyethylene,which makes biodegradable polymers more difficult to spread or sprayonto a fibrous sheet. It may therefore be advantageous to incorporateone or more of water, solvent, or plasticizer, and/or increase thetemperature of the biodegradable polymer or polymer blend well above itssoftening temperature or range, but without burning or otherwise harmingit, to increase its MFI so as to facilitate the coating or impregnatingprocess.

[0029] In one preferred embodiment, 4-5 lb/1000 ft² (12-15 lb/3000 ft²)tissue paper is treated with a biodegradable polymer blend to render itmore resistant to penetration by liquids. Of course, it is certainlywithin the scope of the invention to utilize any weight paper or tissuepaper, e.g., tissue paper ranging in weight from 8 lb/3000 ft² up to 60lb/3000 ft². One of the benefits of coating or impregnating a fibroussheet with a biodegradable polymer or polymer blend, as compared tosimply making a sheet or film from the polymer blend itself, is that thefibrous sheet core increases the thermal stability of the resultingarticle of manufacture. This is beneficial in the case of wraps becauseincreasing the thermal stability increases their ability to bemicrowaved without degrading or melting onto the food that is wrappedtherein.

[0030] Increasing the amount of inorganic fillers within thebiodegradable polymer or polymer blend used to coat or impregnate afibrous sheet also increases the microwaveability of the resultingwraps. Providing biodegradable polymer wraps that are microwaveable isan improvement over wraps made using polyethylene, which are neitherbiodegradable nor microwave safe.

[0031] These and other advantages and features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order that the manner in which the above-recited and otheradvantages and objects of the invention are obtained, a more particulardescription of the invention briefly described above will be rendered byreference to a specific embodiment thereof which is illustrated in theappended drawings. Understanding that these drawings depict only atypical embodiment of the invention and are not therefore to beconsidered to be limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings, in which:

[0033]FIG. 1 is a plot of the percent elongation at break versus theapplied strain rate for various neat and blended polymer films;

[0034]FIG. 2 is a plot of the percent elongation of various neat polymerand blended polymer films versus the concentration of ECOFLEX within thefilms at a fixed strain rate of 500 mm/min.;

[0035]FIG. 3 is a plot of the percent elongation of various neat polymerand blended polymer films versus the concentration of ECOFLEX within thefilms at a fixed strain rate of 1000 mm/min.;

[0036]FIG. 4 is a plot of the break stress versus the applied strainrate for various neat and blended polymer films;

[0037]FIG. 5 is a plot of the break stress of various neat polymer andblended polymer films versus the concentration of ECOFLEX within thefilms at a fixed strain rate of 500 mm/min.;

[0038]FIG. 6 is a plot of the break stress of various neat polymer andblended polymer films versus the concentration of ECOFLEX within thefilms at a fixed strain rate of 1000 mm/min.;

[0039]FIG. 7 is a plot of the Water Vapor Permeability Coefficients(WVPC) of various neat polymer and blended polymer films as a functionof the concentration of ECOFLEX within the films, and an estimated trendline based on the lowest measured WVPC for a neat ECOFLEX film of7.79×10⁻³ g•cm/m²/d/mm Hg;

[0040]FIG. 8 is a plot of the Water Vapor Permeability Coefficients(WVPC) of various neat polymer and blended polymer films as a functionof the concentration of ECOFLEX within the films, and an estimated trendline based on the highest measured WVPC for a neat ECOFLEX film of42×10⁻³ g•cm/m²/d/mm Hg; and

[0041]FIG. 9 is a plot of the modulus of various neat polymer andblended polymer films versus the concentration of ECOFLEX within thefilms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Introduction

[0042] The invention relates to fibrous sheets that are coated orimpregnated with inventive biodegradable polymers or polymer blends. Thetreated fibrous sheets according to the invention are in many wayssuperior to conventional plastics that suffer from their inability todegrade when discarded into the environment, that are not readilyprintable absent special treatment, and that generally have poordead-fold properties. The treated sheets can be engineered to haveimproved strength, flexibility, elongation, temperature stability,microwaveability, processability, and dead-fold.

[0043] In one aspect of the invention, a biodegradable polymer blendused to treat fibrous sheets includes at least one biopolymer havingrelatively high stiffness and at least one biopolymer having relativelyhigh flexibility. When blended together, it is possible to derive thebeneficial properties from each polymer while offsetting or eliminatingthe negative properties of each polymer when used separately.

[0044] In another aspect of the invention, one or more biodegradablepolymers used to coat a fibrous sheet are blended with a significantquantity of an inorganic filler in order to greatly increase the heatstability of the resulting treated sheet. Fibrous sheets themselves tendto have greater heat stability compared to sheets and films formed usingbiodegradable polymers. Adding an inorganic filler to the biodegradablepolymer or polymer blend (e.g., in a concentration of at least about 30%by weight of the biodegradable polymer composition used to coat orimpregnate the fibrous sheet) further increases the heat stability oftreated sheets according to the invention. In the case of wraps used toprotect food, such wraps can better withstand hot foods and beingmicrowaved.

[0045] The treated sheets according to the invention are suitable foruse as packaging materials, such as wraps, bags, pouches, coverings,laminate coatings, cartons, jugs, cups, plates, bowls, trays, platters,lids, straws, and the like.

[0046] Biodegradable polymers that may be used to treat fibrous sheetsaccording to the present invention include, but are not limited to,synthetic polyesters, naturally derived polyesters, polyester amides,polycarbonates, and polyester urethanes, but may also include a varietyof natural polymers and their derivatives, such as polymers andderivatives of starch, cellulose, other polysaccharides, and proteins.Particulate fillers, both organic and inorganic, may be incorporatedinto the polymers used to treat fibrous sheets to improve the dead-foldproperties, increase bulk hand feel, create cavitation, reduce cost,and/or decrease self-adhesion of the treated sheets. Plasticizers may beadded to impart desired softening and elongation properties. Treatedfibrous sheets may optionally be embossed, crimped, quilted or otherwisetextured to improve bulk hand feel and dead-fold. The biopolymers andbiopolymer blends according to the invention more readily accept andretain print compared to conventional plastics or waxed papers becausethey typically include oxygen-containing moieties, such as ester, amide,or urethane groups, to which inks can readily adhere.

[0047] The terms “sheets” and “films” are to be understood as havingtheir customary meanings as used in the thermoplastic and packaging artsNevertheless, because the distinction between what constitutes a “sheet”and what constitutes a “film” largely turns on the thickness of thearticle of manufacture, the distinction is somewhat arbitrary (i.e. somearticles may constitute both sheets and films). Because thebiodegradable compositions according to the invention can be used tomanufacture a wide variety of articles of manufacture, includingarticles useful to wrap, package or otherwise package food or othersolid substrates, including sheets and films having a wide variety ofthicknesses (both measured and calculated), it is not the intention ofthis disclosure to precisely distinguish, in all cases, between what mayarguably constitute a “sheet” versus articles that may arguablyconstitute a “film”. Therefore, when the present disclosure refers to“sheets and films” and “sheets or films”, the intention is to designatethe entire universe of articles of manufacture that may arguablyconstitute “sheets”, “films” or both.

[0048] The terms “polymer blend” and “biodegradable polymer composition”includes two or more unfilled polymers and/or one or more polymers intowhich one or more types of solid fillers have been added.

[0049] The term “microwaveable” refers to biodegradable polymercompositions and treated sheets that can be placed together with foodinto a microwave oven and microwaved so as to heat the food without thecomposition melting or otherwise transferring from the treated sheetonto the food.

II. Treated Sheets

[0050] Treated sheets according to the invention include any fibroussheet that has been coated or impregnated with a biodegradable polymerblend to render the fibrous sheet more resistant to liquids, such aswater, oils or solvents. Specific examples of fibrous sheets andbiodegradable polymer blends that may be used to manufacture treatedsheets within the scope of the invention will now be discussed ingreater detail.

[0051] A. Fibrous Sheets

[0052] It is within the scope of the invention to coat or impregnatevarious fibrous sheets known in the art. Examples include a wide varietyof tissue papers, ordinary paper, paperboard, felts, wovens andnonwovens. In one embodiment, the fibrous sheet comprises a 12-15lb/3000 ft² tissue paper. Coating or impregnating 12-15 lb/3000 ft²tissue paper yields treated sheets that are especially suitable for useas food wraps. It will be appreciated that it is within the scope of theinvention to treat tissue papers and papers having a wide range ofpossible weights, e.g., from 8 lb/3000 ft² to 60 lb/3000 ft².

[0053] B. Biodegradable Polymers.

[0054] Biodegradable polymers that may be used within the scope of thepresent invention to coat or impregnate fibrous sheets include thosewhich degrade through the action of living organisms, light, air, waterand combinations of the foregoing. Such polymers include a range ofsynthetic polymers, such as polyesters, polyester amides, polycarbonatesand the like. Naturally-derived semi-synthetic polyesters (e.g. fromfermentation) can also be used. Biodegradation reactions are typicallyenzyme-catalyzed and generally occur in the presence of moisture.Natural macromolecules containing hydrolyzable linkages, such asprotein, cellulose and starch, are generally susceptible tobiodegradation by the hydrolytic enzymes of microorganisms. A fewman-made polymers, however, are also biodegradable. Thehydrophilic/hydrophobic character of polymers greatly affects theirbiodegradability, with more polar polymers being more readilybiodegradable as a general rule. Other characteristics that affectpolymer biodegradability include crystallinity, chain flexibility andchain length.

[0055] Besides being able to biodegrade, it is often important for apolymer or polymer blend to exhibit certain physical properties, such asstiffness, flexibility, water-resistance, oil-resistance, solventresistance, strength, elongation, temperature stability, moisture vaportransmission, gas permeability, and/or dead-fold. The intendedapplication of a particular treated fibrous sheet will often dictatewhich properties are necessary in order for a particular polymer,polymer blend, or treated sheet manufactured therefrom to exhibit thedesired performance criteria. When used to form treated sheets suitablefor use as packaging materials, desired performance criteria may includeelongation, dead-fold, strength, printability, imperviousness toliquids, breathability, temperature stability, and the like.

[0056] Because of the limited number of biodegradable polymers, it isoften difficult, or even impossible, to identify one single polymer orcopolymer which meets all, or even most, of the desired performancecriteria for a given application. This is particularly true in the areaof packaging materials. Polymers that have a high glass transitiontemperature (T_(g)) are often difficult, if not impossible, to blow orcast into films on a mass scale. On the other hand, polymers that have avery low glass transition temperature typically have relatively lowsoftening and/or melting points, which makes them difficult to massproduce into sheets and films without the tendency of blocking, or selfadhesion. Moreover, such sheets and films may lack adequate strength,water vapor barrier properties, high temperature stability, and/ormodulus to be suitable for certain applications, such as in themanufacture of wraps or laminates coatings.

[0057] In one aspect of the invention, it has been discovered thatcompositions suitable for coating or impregnating fibrous sheets can beobtained by blending one or more “stiff”, or high glass transitiontemperature, polymers with one or more “soft”, or low glass transitiontemperature, polymers. In another aspect of the invention, polymers orpolymer blends can be filled with particulate fillers, and/or treatedsheets or films made therefrom can be textured, in order to yield sheetshaving improved dead-fold properties.

[0058] Notwithstanding the benefits that can be derived from using ablend of stiff and soft polymers, particularly when extruding or blowingfilms or sheets used to coat fibrous sheets, it will be appreciated thatthere are coating methods that do not require the formation of anextruded or blown film or sheet, such as spreading using a doctor bladeor spray coating. In such cases, it may not be necessary to use apolymer blend. It may be desirable, however, to use water, a solvent, orplasticizer to increase the MFI to facilitate the coating orimpregnation process. It may be desirable to incorporate a significantquantity of an inorganic filler (e.g. silica or limestone) in order toincrease the heat stability of the resulting treated sheet. In the caseof a food wrap, increasing the heat stability increases themicrowaveability of the treated sheet.

[0059] 1. Stiff Polymers.

[0060] Even though the use of terms such as “stiff” and “soft” polymersmay be somewhat arbitrary, such classifications are useful whendetermining which polymers to blend together in order to obtain apolymer blend having the desired performance criteria. In general, thosepolymers that may be characterized as being relatively “stiff”, or lessflexible, typically include polymers which have a glass transitiontemperature of at least about 10° C. Stiff polymers will preferably havea glass transition temperature of at least about 15° C., more preferablyat least about 25° C., and most preferably at least about 35° C. Theforegoing temperatures attempt to take into consideration the fact thatthe “glass transition temperature” is not always a discreet temperaturebut is often a range of temperatures within which the polymer changesfrom being a glassy and more brittle material to being a softer and moreflexible material.

[0061] The glass transition temperature should be distinguished from themelting point of a polymer at or beyond which a thermoplastic polymerbecomes plastic and deformable without significant rupture. Althoughthere is often a positive correlation between a polymer's glasstransition temperature (T_(g)) and its melting point (T_(m)), this isnot strictly the case with all polymers. In some cases the differencebetween T_(g) and T_(m) may be large. In other cases it may berelatively small. It is generally the case, however, that the meltingpoint of a stiffer polymer will typically be greater than the meltingpoint of a softer polymer.

[0062] Preferred “stiff” polymers include, but are not limited to,modified polyethylene terephthalates (such as those manufactured by DuPont), polyesteramides (such as those manufactured by Bayer), polylacticacid-based polymers (such as those manufactured by Cargill-Dow Polymersand Dianippon Ink), terpolymers based on polylactic acid, polyglycolicacid and polycaprolactone (such as those manufactured by MitsuiChemicals), polyalkylene carbonates (such as polyethylene carbonatemanufactured by PAC Polymers), and polyhydroxybutyrate (PHB).

[0063] A presently preferred stiff biopolymer includes a range ofmodified polyethylene terephthalate (PET) polymers manufactured byDuPont, and sold under the trade name BIOMAX. Various modified PETpolymers of DuPont are described in greater detail in U.S. Pat. No.5,053,482 to Tietz, U.S. Pat. No. 5,097,004 to Gallagher et al., U.S.Pat. No. 5,097,005 to Tietz, U.S. Pat. No. 5,171,308 to Gallagher etal., U.S. Pat. No. 5,219,646, to Gallagher et al., and U.S. Pat. No.5,295,985 to Romesser et al. For purposes of disclosing “stiff”polymers, the foregoing patents are disclosed herein by reference.

[0064] In general, the modified PET polymers of DuPont may becharacterized as comprising alternating units of a terephthalateconstituent and an aliphatic constituent, with the aliphatic constituentcomprising a statistical distribution of two or more different aliphaticunits derived from two or more different diols, such as ethylene glycol,diethylene glycol, triethylene oxide, polyethylene glycol, lower alkanediols, both branched and unbranched, and derivatives of the foregoing. Aportion of the aliphatic units may also be derived from an aliphaticdiacid, such as adipic acid. In addition, a fraction of the phenylenegroups within the repeating terephthalate units may be sulfonated andneutralized with an alkali metal or alkaline earth metal base. Both thealiphatic portion of the modified PET polymer as well as thestatistically significant quantity of sulfonated terephthalate unitscontribute significantly to the biodegradability of the BIOMAX polymer.

[0065] Some BIOMAX grades of polymers have a melting point of 200-208°C. and a glass transition temperature of 40-60° C. BIOMAX 6926 is onesuch grade. It is a relatively strong and stiff polymer that, whenblended with a softer polymer, yields a mixture that can readily beformed into sheets and films. In addition, or in the alternative, one ormore particulate fillers may be included in order to impart desiredproperties described more fully herein.

[0066] In general, modified polyethylene terephthalates that would beexpected to have properties suitable for use as a “stiff” biodegradablepolymer consist essentially of recurring structural units having thefollowing general formula:

—[—C(O)R—C(O)—OGO—]_(a)—[—C(O)—Q—O—]_(b)—

[0067] wherein up to about 40 mole % of R is selected from the groupconsisting of a chemical bond and one or more divalent, non-aromatic,C₁-C₁₀ hydrocarbylene radicals, and the remainder of R is at least about85% mole % p-phenylene radical,

[0068] wherein G includes from 0 to about 30 mole % of a polyethyleneether radical selected from the group consisting of:

—(CH₂)₂—O—(CH₂)₂—

[0069] and

—CH₂)₂—O—(CH₂)₂—O—(CH₂)₂—

[0070] and the remainder of G is selected from the group consisting ofpolyalkylene ether radicals of molecular weight at least about 250(number average), and —(CH₂)₂—, —(CH₂)₃—, and —(CH₂)₄— radicals,

[0071] wherein Q is derived from a hydroxy acid of the formula:

HO[—C(O)—Q—O—]_(x)H

[0072] wherein x is an integer and such hydroxy acids have a meltingpoint at least 5° C. below their decomposition temperature, and Q isselected from the group consisting of a chemical bond and hydrocarbyleneradicals —(CH₂)_(n)—, where n is an integer from 1 to 5, —C(R′)H—, and—C(R′)HCH₂—. wherein R′ is selected from the group consisting of —CH₃and —CH₂CH₃, and wherein “a” and “b” are mole fractions of the polymer,and the mole fraction “a” may be 0.6 to 1 and, correspondingly, molefraction “b” may be 0 to 0.4, and wherein about 0.1 to about 15 mole %,preferably about 0.1 to about 2.5 mole %, of the polymer contains alkalimetal or alkaline earth metal sulfo groups, especially about 1.5 toabout 2 mole % of such groups.

[0073] Another stiff biopolymer that may be used in manufacturingpolymer blends according to the present invention includes polylacticacid (PLA). Polylactic acid typically has a glass transition temperatureof about 59° C. and a melting point of about 178° C. PLA has lowelongation and is quite hard. It is a strong thermoplastic material thatcan be injection molded, extruded, cast, thermoformed, or used as spunor melt-blown fibers to produce nonwoven goods.

[0074] Polymers based on or including PLA first found commercialapplication as medical sutures in 1970. High polymers of lactic acid(M_(n)=50,000-110,000) are strong thermoplastics that can be fabricatedinto useful products that can be broken down by common soil bacteria.Potential applications of PLA include paper coatings for packaging (foodand beverage cartons), plastic foam for fast foods, microwavablecontainers, and other consumer products such as disposable diapers oryard waste bags. PLA can be a homopolymer or it may be copolymerizedwith glycolides, lactones or other monomers. One particularly attractivefeature of PLA-based polymers is that they are derived from renewableagricultural products.

[0075] Because lactic acid is difficult to polymerize directly to highpolymers in a single step on a commercial scale, most companies employ atwo-step process. Lactic acid is first oligomerized to a linear chainwith a molecular weight of less than 3000 by removing water. Theoligomer is then depolymerized to lactide, which is a cyclic dimerconsisting of two condensed lactic acid molecules. This six-member ringis purified and subjected to ring opening polymerization to producepolylactic acid with a molecular weight of 50,000-110,000.

[0076] Because lactic acid has an asymmetric carbon atom, it exists inseveral isomeric forms. The lactic acid most commonly sold commerciallycontains equal parts of L-(+)-lactic acid and D-(−)-lactic acid and istherefore optically inactive, with no rotatory power. The racemicmixture is called DL-lactic acid.

[0077] Another stiff polymer that may be used within the inventivepolymer blends is known as CPLA, which is a derivative of PLA and issold by Dianippon Ink. Two classes of CPLA are sold and are referred toas “CPLA hard” and “CPLA soft”, both of which comprise “stiff polymers”,as that term has been defined herein. CPLA hard has a glass transitiontemperature of 60° C., while CPLA soft has a glass transitiontemperature of 51° C.

[0078] Bayer corporation manufactures polyesteramides sold under thename BAK. Polyester amides manufactured by Bayer are described morefully in U.S. Pat. No. 5,644,020 to Timmermann et al. For purposes ofdisclosing biodegradable polymers, at least some of which constitute“stiff” polymers, the foregoing patent is incorporated herein byreference. One form of BAK is prepared from adipic acid, 1,4-butanediol,and 6-aminocaproic acid. BAK 1095, a polyesteramide having an M_(n) of22,700 and an M_(w) of 69,700 and which contains aromatic constituents,has a melting point of 125° C. BAK 2195 has a melting point of 175° C.Although the glass transition temperatures of BAK 1095 and BAK 2195 aredifficult to measure, because BAK appears to behave like a stiff polymerin the sense that improved properties may be obtained by blending BAKwith a soft polymer, the inventors believe that the glass transitiontemperature of BAK polymers is essentially at least about 10° C. Forpurposes of understanding the meaning and scope of the specification andclaims, polyester amides such as BAK, as well as others that behave likeBAK and can be used as a “stiff” polymer, shall be deemed to have aglass temperature of at least about 10° C.

[0079] Mitsui Chemicals, Inc. manufactures a terpolymer that includesunits derived from polylactide, polyglycolide and polycaprolactone thathave been condensed together. Thus, this polymer is an aliphatic polymerand may be characterized as a PLA/PGA/PCL terpolymer. Three grade ofthis polymer are available, H100J, S100 and T100. The H100J gradePLA/PGA/PCL terpolymer has been analyzed to have a glass transitiontemperatures of 74° C. and a melting point of 173° C.

[0080] PAC Polymers Inc. manufactures polyethylene carbonate (PEC)having a glass transition temperature range of 10-28° C. PEC is a“stiff” polymer for purposes of the present invention.

[0081] Polyhydroxybutyrates (PHBs) can act as either a stiff or softpolymer depending on their molecular weight, whether they have beenmodified using chain extenders and/or branching agents, whether theyhave been copolymerized with another polymer, and depending on the otherconstituents within the overall thermoplastic composition. In thissense, PHBs are unique among biopolymers and may be of special interestfor use in making wraps, laminate coatings, packaging materials, and thelike.

[0082] As discussed more fully below, native or dried gelatinized starchcan be used as particulate fillers in order to increase the dead-foldproperties of sheets and films made from a particular polymer or polymerblend. However, to the extent that starches become thermoplastic butretain a substantially portion of their crystallinity, such starches mayact as “stiff”, rather than “soft”, polymers.

[0083] 2. Soft Polymers.

[0084] In general, those biopolymers that may be characterized as being“soft”, or less rigid, typically include polymers which have a glasstransition temperature of less than about 0° C. Soft biopolymers withinthe scope of the invention will typically have a glass transitiontemperature of less than about 0° C., preferably less than about 4° C.,more preferably less than about −10° C., more especially preferably lessthan about −20° C., and most preferably less than about −30° C. Theforegoing temperatures attempt to take into consideration the fact thatthe “glass transition temperatures” of “soft” polymers are not alwaysdiscreet temperatures but often comprise a range of temperatures.

[0085] Preferred “soft” biopolymers within the scope of the presentinvention include, but are not limited to, aliphatic-aromaticcopolyesters (such as those manufactured by BASF and Eastman Chemical),aliphatic polyesters which include repeating units having at least 5carbon atoms, e.g., polyhydroxyvalerate,polyhydroxybutyrate-hydroxyvalerate copolymer and polycaprolactone (suchas those manufactured by Daicel Chemical, Monsanto, Solvay, and UnionCarbide), and succinate-based aliphatic polymers, e.g., polybutylenesuccinate (PBS), polybutylene succinate adipate (PBSA), and polyethylenesuccinate (PES) (such as those manufactured by Showa High Polymer).

[0086] U.S. Pat. Nos. 5,817,721, 5,863,991, 5,880,220, 5,889,135,5,936,045, 6,018,004, 6,046,248, 6,111,058, 6,114,042, 6,201,034,6,258,924, 6,297,347, 6,303,677, 6,353,084, all to Warzelhan et al., andassigned to BASF, disclose a range of aliphatic-aromatic copolyesterswithin the scope of the invention, as do U.S. Pat. No. 6,103,058 toYamamoto et al. and U.S. Pat. No. 6,120,895 to Kowitz et al. Similarly,U.S. Pat. Nos. 5,292,783, 5,446,079, 5,559,171, 5,580,911, 5,599,858 and5,900,322, all to Buchanan et al. and assigned to Eastman Chemical, aswell as U.S. Pat. Nos. 6,020,393 and 6,922,829 to Khemani, also assignedto Eastman Chemical, disclose aliphatic-aromatic copolyesters within thescope of the invention. For purposes of disclosing “soft” polymers, theforegoing patents are incorporated herein by reference.

[0087] A preferred “soft” polymer that may be used in the manufacture ofpolymer blends includes aliphatic-aromatic copolyesters manufactured byBASF and sold under the trade name ECOFLEX. The aliphatic-aromaticcopolyesters manufactured by BASF comprise a statistical copolyesterderived from 1,4-butanediol, adipic acid, and dimethylterephthalate(DMT). In some cases, a diisocyanate is used as a chain lengthener.Branching agents may also be used to yield branched, rather than linear,copolymers.

[0088] Copolymerization of aliphatic monomers, such as diols anddiacids, with aromatic monomers, such as diols and diacids (e.g.,terephthalic acid or diester derivatives such as DMT), is one way toimprove the performance properties of aliphatic polyesters. However,questions have been raised within the industry regarding the completebiodegradability of aliphatic-aromatic copolyesters because aromaticcopolyesters such as PET are known to be resistant to microbial attack.Nevertheless, researchers have discovered that aliphatic-aromaticcopolyesters are indeed biodegradable and that the biodegradability ofthese copolyesters is related to the length of the aromatic sequence.Block copolyesters with relatively long aromatic sequences are lessrapidly degraded by microorganisms compared to random copolyestershaving more interrupted aromatic sequences. Film thickness is also afactor, with thicker films degrading more slowly due to their reducedsurface to volume ratio than thinner films, all things being equal. Thepolymer presently sold under the name ECOFLEX S BX 7000 by BASF has aglass transition temperature of −33° C. and a melting range of 105-115°C.

[0089] Another “soft” aliphatic-aromatic copolyester is manufactured byEastman Chemical Company and is sold under the trade name EASTAR BIO.The aliphatic-aromatic copolyester manufactured by Eastman is a randomcopolymer derived from 1,4-butanediol, adipic acid, anddimethylterephthalate (DMT). One particular grade of EASTAR BIO, knownas EASTAR BIO 14766, has a glass transition temperature of −33° C. and amelting point of 112° C. It has a tensile strength at break in themachine direction of 19 MPa, an elongation at break of 600%, and atensile modulus of elasticity of 97 MPa (tangent). It has an Elmendorftear strength of 282 g.

[0090] Polycaprolactone (PCL) is a biodegradable aliphatic polyesterhaving a relatively low melting point and a very low glass transitiontemperature. It is so named because it is formed by polymerizingε-caprolactone. The glass transition temperature of PCL is −60° C. andthe melting point is only 60° C. Because of this PCL and other similaraliphatic polyesters with low melting points are difficult to process byconventional techniques such as film blowing and blow molding. Filmsmade from PCL are tacky as extruded and have low melt strength over 130°C. Also, the slow crystallization of this polymer causes the propertiesto change over time. Blending PCL with other polymers improves theprocessability of PCL. One common PCL is TONE, manufactured by UnionCarbide. Other manufactures of PCL include Daicel Chemical, Ltd. andSolvay. Though the use of PCL is certainly within the scope of theinvention, it is currently a less preferred soft biopolymer thanaliphatic-aromatic polyesters, which give overall better performance.

[0091] ε-Caprolactone is a seven member ring compound that ischaracterized by its reactivity. Cleavage usually takes place at thecarbonyl group. ε-Caprolactone is typically made from cyclohexanone by aperoxidation process. PCL is a polyester made by polymerizingε-caprolactone. Higher molecular weight PCL may be prepared under theinfluence of a wide variety of catalysts, such as aluminum alkyls,organometallic compositions, such as Group Ia, IIa, IIb, or IIIa metalalkyls, Grignard reagents, Group II metal dialkyls, calcium or othermetal amides or alkyl amides, reaction products of alkaline earthhexamoniates, alkaline oxides and acetonitrile, aluminum trialkoxides,alkaline earth aluminum or boron hydrides, alkaline metal or alkalineearth hydrides or alkaline metals alone. PCL is typically prepared byinitiation with an aliphatic diol (HO—R—OH), which forms a terminal endgroup.

[0092] Another “soft” aliphatic polyester that may be used inmanufacturing the inventive polymer blends ispolyhydroxybutyrate-hydroxyvalerate copolymer (PHBV), which ismanufactured using a microbial-induced fermentation process. One suchPHBV copolyester, manufactured by the Monsanto Company, has a glasstransition temperature of about 0° C. and a melting point of about 170°C. If possible, PHBV copolyesters should be formulated and/or modifiedso as have a glass transition temperature less than about −5° C.

[0093] In the fermentation process used to manufacture PHBV, a singlebacterium species converts corn and potato feed stocks into a copolymerof polyhydroxybutyrate and hydroxyvalerate constituents. By manipulatingthe feed stocks, the proportions of the two polymer segments can bevaried to make different grades of material. All grades are moistureresistant while still being fully biodegradable. The world producers ofPHBV are Monsanto, with its BIOPOL product, and METABOLIX, with itsvarious grades of polyhydroxy-alkanoates (PHAs). Polyhydroxyvalerate(PHV) is also an example of a “soft” polymer.

[0094] As set forth above, polyhydroxybutyrates (PHBs) can act as eithera stiff or soft polymer depending on their molecular weight, whetherthey have been modified using chain extenders and/or branching agents,whether they have been copolymerized with another polymer, and dependingon the other constituents within the overall thermoplastic composition.In this sense, PHBs are unique among biopolymers and may be of specialinterest for use in making wraps, laminate coatings, packagingmaterials, and the like.

[0095] Another class of “soft” aliphatic polyesters are based onrepeating succinate units such as polybutylene succinate (PBS),polybutylene succinate adipate (PBSA), and polyethylene succinate (PES).Each of these succinate-based aliphatic polyesters are manufactured byShowa High Polymer, Ltd. and are sold under the trade name BIONELLE. PBS(Bionolle 1001) has a glass transition temperature of −30° C. and amelting point of 114° C. PBSA (Bionolle 3001) has a glass transitiontemperature of −35° C. and a melting point of 95° C. PES (Bionolle 6000)has a glass transition temperature of −4° C. and a melting point of102°.

[0096] The target applications for BIONOLLE include films, sheets,filaments, foam-molded products and foam-expanded products. BIONOLLE isbiodegradable in compost, in moist soil, in water with activated sludge,and in sea water. PBSA degrades rapidly in a compost environment, so itis similar to cellulose, whereas PBS degrades less rapidly and issimilar to newspaper in terms of biodegradation.

[0097] BIONOLLE is manufactured according to a patented two-step processof preparing succinate aliphatic polyesters with high molecular weightsand useful physical properties. In a first step, a low molecular weighthydroxy-terminated aliphatic polyester prepolymer is made from a glycoland an aliphatic dicarboxylic acid. This polymerization is catalyzed bya titanium catalyst such as tetraisopropyltitanate, tetraisopropoxytitanium, dibutoxydiacetoacetoxy titanium, or tetrabutyltitanate. In thesecond step, a high molecular weight polyester is made by reacting adiisocyanate, such as hexamethylene diisocyanate (HMDI) with a polyesterprepolymer.

[0098] Showa manufactures PBS by first reacting 1,4-butanediol withsuccinic acid in a condensation reaction to form a prepolymer and thenreacting the prepolymer with HMDI as a chain extender.

[0099] PBSA copolymer is manufactured by first condensing1,4-butanediol, succinic acid and adipic acid to form a prepolymer andthen reacting the prepolymer with HMDI as a chain extender.

[0100] PES homopolymer is prepared by reacting ethylene glycol andsuccinic acid and using HMDI or diphenylmethane diisocyanate as a chainextender.

[0101] Succinate-based aliphatic polyesters are also manufactured byMitsui Toatsu, Nippon Shokubai, Cheil Synthetics, Eastman Chemical, andSunkyon Industries.

[0102] Finally, although starch, such as modified starch or starch thathas been gelatinized with water and subsequently dried, is known to havea high glass transition temperature (i.e., 70-85° C.) and be verycrystalline at room temperature, certain forms of starch in which thecrystallinity has been greatly reduced or destroyed altogether can havevery low glass transition temperatures and may, in fact, constitute“soft” biodegradable polymers within the scope of the invention. Asdiscussed more fully below, native or dried gelatinized starch can beused as particulate fillers in order to increase the dead-foldproperties of sheets and films made from a particular polymer or polymerblend. Moreover, to the extent that starches become thermoplastic butretain a substantially portion of their crystallinity, such starches mayact as “stiff”, rather than “soft”, polymers. Nevertheless, there existsa range of thermoplastic starch polymers that can behave as “soft”polymers.

[0103] For example, U.S. Pat. No. 5,362,777 to Tomka is a landmarkpatent and was the first attempt to manufacture what is known asthermoplastically processable starch (TPS). TPS is characterized as athermoplastic starch polymer formed by mixing and heating native ormodified starch in the presence of an appropriate high boilingplasticizer (such as glycerin and sorbitol) in a manner such that thestarch has little or no crystallinity, a low glass transitiontemperature, and very low water (less than 5%, preferably less thanabout 1% by weight while in a melted state after venting and prior toconditioning). When blended with appropriate hydrophobic polymers, suchas the stiff polymers disclosed herein, e.g., polyesteramides such asBAK, TPS can have a glass transition temperature as low as −60° C., andtypically below about −20° C.

[0104] Although it is within the scope of the invention to includethermoplastic polymers based on starch that include plasticizers such asglycerine, sorbitol, propylene glycol and the like, it is preferable,when manufacturing packaging materials that will come into contact withfood products, to utilize thermoplastic starch polymers that are madewithout the use of such plasticizers, which can potentially diffuse intofood. Preferred thermoplastic starch polymers for use in making foodwraps may advantageously utilize the natural water content of nativestarch granules to initially break down the granular structure and meltthe native starch. Thereafter, the melted starch can be blended with oneor more synthetic biopolymers, and the mixture dried by venting, inorder to yield a final polymer blend. Where it is desired to make foodwraps or other sheets or films intended to contact food using athermoplastic starch polymer made with a high boiling liquidplasticizer, it will be preferable to limit the quantity of suchthermoplastic starch polymers to less than 10% by weight of the polymermixture, exclusive of any solid fillers.

[0105] C. Other Components.

[0106] There are a number of optional components which may be includedwithin the biodegradable polymer blends in order to impart desiredproperties. These include, but are not limited to, plasticizers,lubricants, fillers, natural polymers and nonbiodegradable polymers.

[0107] 1. Plasticizers and Lubricants.

[0108] Plasticizers and lubricants may optionally be added in order toimprove processing, such as extrusion, film blowing, spreading orspraying, or final mechanical properties, particularly of polymer blendsthat are relatively stiff. A stiffer polymer blend may be dictated byother performance criteria, such as high temperature stability,strength, lower elongation, higher dead-fold, resistance to “blocking”during and after processing, and the like. In such cases, a plasticizermay allow the polymer blend to satisfy certain processing and/orperformance criteria.

[0109] In the case where a biodegradable polymer or polymer blend isspread or sprayed onto a fibrous sheet, it may be advantageous to use aplasticizer to increase the melt flow index (MFI) of the molten polymeror polymer blend. Increasing the MFI of a molten polymer or polymerblend facilitates high speed coating. In general, when certainbiodegradable polymers are heated to above their softening point, theyhave an MFI between about 2-10 g/10 min. Increasing the MFI preferablyto at least about 40 g/10 min., more preferably to at least about 70g/10 min., and most preferably to at least about 100 g/10 min. greatlyfacilitates spreading or spraying a molten biodegradable polymer blend.

[0110] Suitable plasticizers within the scope of the invention,particularly when incorporated into a polymer blend that is intended tobe used in the manufacture of wraps and other packaging materials thatwill come into contact with food, will preferably be safe if consumed,at least in smaller quantities.

[0111] Exemplary plasticizers that may be used in accordance with thepresent invention include, but are not limited to, soybean oil, casteroil, TWEEN 20, TWEEN 40, TWEEN 60, TWEEN 80, TWEEN 85, sorbitanmonolaurate, sorbitan monooleate, sorbitan monopalmitate, sorbitantrioleate, sorbitan monostearate, PEG, derivatives of PEG, N,N-ethylenebis-stearamide, N,N-ethylene bis-oleamide, polymeric plasticizers suchas poly(1,6-hexamethylene adipate), and other compatible low molecularweight polymers.

[0112] Examples of lubricants include salts of fatty acids, an exampleof which is magnesium stearate.

[0113] Volatile plasticizers that can be removed during or after thecoating process, such as water or volatile solvents, may be used tofacilitate high speed coating. Examples of volatile solvents that may beused, preferably by recovering and reusing such solvents, include, butare not limited to, chloroform, methylene chloride, other chlorinatedhydrocarbons, ethyl alcohol, isopropyl alcohol, other alcohols, acetone,methyl ethyl ketone, other ketones, and the like.

[0114] It has been found, for example, that including 200 ppm waterincreases the MFI of a molten biodegradable polymer composition from 4g/10 min. to about 40 g/10 min. Whereas many of the biodegradablepolymers described herein are “hydrophobic” in the sense that they donot dissolve or degrade when exposed to water at room temperature, theydo contain polar moieties that greatly increase the affinity of suchpolymers for water while heated to a molten state. Thus, it is possibleto blend some amount of water within molten a biodegradable polymer thatwould otherwise be hydrophobic when cooled to room temperature.

[0115] 2. Solid Fillers.

[0116] Particulate fillers may optionally be added for a number ofreasons, including but not limited to, increasing the Young's modulus,dead-fold properties, rigidity, breathability, thermal stability,microwaveability, and insulating ability, and for decreasing the costand tendency of the polymer blend to “block” or self-adhere duringprocessing. Other fillers, like fibers having a high aspect ratio, mayincrease the strength, fracture energy and dead-fold properties of thesheets and films according to the invention. In general, fillers withinthe scope of the invention will generally fall within three classes orcategories: (1) inorganic particulate fillers, (2) fibers and (3)organic fillers.

[0117] a. Inorganic Particulate Fillers

[0118] The terms “particle” or “particulate filler” should be broadlyinterpreted to include filler particles having any of a variety ofdifferent shapes and aspect ratios. In general, “particles” are thosesolids having an aspect ratio (i.e., the ratio of length to thickness)of less than about 10:1. Solids having an aspect ratio greater thanabout 10:1 may be better understood as “fibers”, as that term will bedefined and discussed hereinbelow.

[0119] Virtually any known filler, whether inert or reactive, can beincorporated into the biodegradable polymer blends. In general, addingan inorganic filler will tend to reduce the cost of the resultingpolymer blend. If a relatively small amount of inorganic filler is used,the effects on the properties of the final composition are minimized,while adding a relatively large amount of inorganic filler will increasethose effects. In those cases where adding the inorganic filler willtend to detract from a critical physical parameter, such as tensilestrength or flexibility, only so much of the filler should be added inorder to reduce the cost of the resulting composition, while retainingadequate mechanical properties required by the intended use. However, inthose cases where adding the inorganic filler will improve one or moredesired physical properties of a given application, such as stiffness,compressive strength, dead-fold, heat resistance, microwaveability,insulating ability, and/or breathability, it may be desirable toincrease the quantity of added filler in order to provide this desiredproperty while also proving greatly decreased cost.

[0120] It will be appreciated that one of ordinary skill in the art,using a microstructural engineering approach, can select the types andamount of the various inorganic fillers that may be included within thepolymer blend in order to engineer a final material having the desiredproperties while taking advantage of the cost-reducing properties ofadding the inorganic filler.

[0121] In general, in order to maximize the quantity of inorganic fillerwhile minimizing the deleterious mechanical effects of adding the filleras much as possible, it may be advantageous to select filler particlesin a manner that decreases the specific surface area of the particles.The specific surface area is defined as the ratio of the total particlesurface area versus the total particle volume. One way to decrease thespecific surface area is to select particles that have a more uniformsurface geometry. The more jagged and irregular the particle surfacegeometry, the greater will be the ratio of surface area to volume ofthat particle. Another way to decrease the specific surface area is toincrease the particle size. In view of the advantages of decreasing thespecific surface area of the inorganic filler, it will be preferable toinclude inorganic filler particles having a specific surface area in arange from about 0.1 m²/g to about 400 m²/g, more preferably in rangefrom about 0.15 m²/g to about 50 m²/g, and most preferably in a rangefrom about 0.2 m²/g to about 2 m²/g.

[0122] Related to decreased specific surface area in improving therheology and final strength properties of the polymer blends of thepresent invention is the concept of particle packing. Particle packingtechniques allow for a reduction in “wasted” interstitial space betweenparticles while maintaining adequate particle lubrication and, hence,mixture rheology, within the melted polymer blend, while also allowingfor more efficient use of the thermoplastic phase as a binder in thefinal hardened polymer blends of the present invention. Simply stated,particle packing is the process of selecting one or more ranges ofparticle sizes in order that the spaces between larger particles aresubstantially occupied by a selected group of smaller particles.

[0123] In order to optimize the packing density of the inorganic fillerparticles, differently sized particles having sizes ranging from assmall as about 0.01 micron to as large as about 2 mm may be used. Ofcourse, the thickness and other physical parameters of the desiredarticle to be manufactured from any given polymer blend may oftendictate the upper particle size limit. In general, the particle packingwill be increased whenever any given set of particles is mixed withanother set of particles having an average particle size (i.e., widthand/or length) that is at least about 2 times bigger or smaller than theaverage particle size of the first group of particles. The particlepacking density for a two-particle system will be maximized whenever thesize ratio of a given set of particles is from about 3-10 times the sizeof another set of particles. Similarly, three or more different sets ofparticles may be used to further increase the particle packing density.

[0124] The degree of packing density that will be “optimal” will dependon a number of factors including, but not limited to, the types andconcentrations of the various components within both the thermoplasticphase and the solid filler phase, the shaping method that will beemployed, and the desired mechanical and other performance properties ofthe final articles to be manufactured from a given polymer blend. One ofordinary skill in the art will be able to determine the optimal level ofparticle packing that will optimize the packing density through routinetesting. A more detailed discussion of particle packing techniques canbe found in U.S. Pat. No. 5,527,387 to Andersen et al. For purposes ofdisclosing particle packing techniques that may be useful in maximizingor optimizing particle packing density, the foregoing patent isincorporated herein by reference.

[0125] In those cases where it is desired to take advantage of theimproved properties of rheology and binding efficiency utilizingparticle packing techniques, it will be preferable to include inorganicfiller particles having a natural particle packing density in a rangefrom about 0.55 to about 0.95, more preferably in range from about 0.6to about 0.9, and most preferably in a range from about 0.7 to about0.85.

[0126] Examples of useful inorganic fillers that may be included withinthe biodegradable polymer blends include such disparate materials assand, gravel, crushed rock, bauxite, granite, limestone, sandstone,glass beads, aerogels, xerogels, mica, clay, alumina, silica, kaolin,microspheres, hollow glass spheres, porous ceramic spheres, gypsumdihydrate, insoluble salts, calcium carbonate, magnesium carbonate,calcium hydroxide, calcium aluminate, magnesium carbonate, titaniumdioxide, talc, ceramic materials, pozzolanic materials, salts, zirconiumcompounds, xonotlite (a crystalline calcium silicate gel), lightweightexpanded clays, perlite, vermiculite, hydrated or unhydrated hydrauliccement particles, pumice, zeolites, exfoliated rock, ores, minerals, andother geologic materials. A wide variety of other inorganic fillers maybe added to the polymer blends, including materials such as metals andmetal alloys (e.g., stainless steel, iron, and copper), balls or hollowspherical materials (such as glass, polymers, and metals), filings,pellets, flakes and powders (such as microsilica).

[0127] The particle size or range of particle sizes of the inorganicfillers will depend on the wall thickness of the film, sheet, or otherarticle that is to be manufactured from the polymer blend. In general,the larger the wall thickness, the larger will be the acceptableparticle size. In most cases, it will be preferable to maximize theparticle size within the acceptable range of particle sizes for a givenapplication in order to reduce the cost and specific surface area of theinorganic filler. For films that are intended to have a substantialamount of flexibility, tensile strength, bending endurance andrelatively low dead-fold and breathability (e.g., plastic bags) theparticle size diameter of the inorganic filler will preferably be lessthan about 20% of the wall thickness of the film. For example, for afilm or sheet having a thickness of 40 microns, it may be preferable forthe inorganic filler particles to have a particle size diameter of about8 microns or less.

[0128] On the other hand, it may be desirable in some cases for at leasta portion of the filler particles to have a larger particle sizediameter, such as a diameter that is equal to or greater than thethickness of the polymeric sheet or film. Utilizing filler particleswhose diameters equal or exceed the thickness of the polymeric sheet orfilm disrupts the surface of the sheet or film and increases the surfacearea, which can advantageously increase the bulk-hand-feel and/ordead-fold properties of the sheet or film. In the case where the sheetsor films are mono or biaxial stretched, the use of larger fillerparticles (e.g., larger than 20% of the wall thickness of the film)creates definitive discontinuities that yield sheets and films having ahigh degree of cavitation. Cavitation results in sheets having a touchand feel that more closely resembles the touch and feel of paper. Inaddition, it greatly increases the breathability and water vaportransmission of the sheets and films.

[0129] The amount of particulate filler added to a polymer blend willdepend on a variety of factors, including the quantity and identities ofthe other added components, as well as the specific surface area,packing density, and/or size distribution of the filler particlesthemselves. Accordingly, the concentration of particulate filler withinthe polymer blends may be included in a broad range from as low as 0% byvolume to as high as about 90% by volume of the polymer blend. Becauseof the variations in density of the various inorganic fillers than canbe used, it may be more correct in some instances to express theconcentration of the inorganic filler in terms of weight percent ratherthan volume percent. In view of this, the inorganic filler componentscan be included within a broad range from as low as 0% by weight to ashigh as 95% by weight of the polymer blend, preferably in a range fromabout 5% to about 90% by weight.

[0130] In those cases where it is desired for the properties of thethermoplastic phase to predominate due to the required performancecriteria of the articles being manufactured, the inorganic filler willpreferably be included in an amount in a range from about 5% to about50% by volume of polymer blend. On the other hand, where it is desiredto create highly inorganically filled systems, the inorganic filler willpreferably be included in an amount in a range from about 50% to about90% by volume.

[0131] In light of these competing objectives, the actual preferredquantity of inorganic filler may vary widely. In general terms, however,in order to appreciably decrease the cost of the resulting polymer blendand/or to impart increased dead-fold, heat-resistance, insulationability, and/or microwaveability, the inorganic filler component willtypically be included in an amount of at least about 10% by weight ofthe overall composition, preferably at least about 15% by weight, morepreferably at least about 20% by weight, more especially preferably atleast about 30% by weight, and most preferably at least about 35% byweight of the overall composition.

[0132] b. Discrete Fibers

[0133] In addition to the fibrous sheet being treated, discrete fiberscan optionally be used in order to improve the physical properties ofthe polymer blends. Like the aforementioned fillers, fibers willtypically constitute a solid phase that is separate and distinct fromthe thermoplastic phase. However, because of the shape of fibers, i.e.,by having an aspect ratio greater than at least about 10:1, they arebetter able to impart strength and toughness than particulate fillers.As used in the specification and the appended claims, the terms “fibers”and “fibrous material” include both inorganic fibers and organic fibers.Fibers may be added to the moldable mixture to increase the flexibility,ductility, bendability, cohesion, elongation ability, deflectionability, toughness, dead-fold, and fracture energy, as well as theflexural and tensile strengths of the resulting sheets and articles.

[0134] Fibers that may be incorporated into the polymer blends includenaturally occurring organic fibers, such as cellulosic fibers extractedfrom wood, plant leaves, and plant stems. In addition, inorganic fibersmade from glass, graphite, silica, ceramic, rock wool, or metalmaterials may also be used. Preferred fibers include cotton, wood fibers(both hardwood or softwood fibers, examples of which include southernhardwood and southern pine), flax, abaca, sisal, ramie, hemp, andbagasse because they readily decompose under normal conditions. Evenrecycled paper fibers can be used in many cases and are extremelyinexpensive and plentiful.

[0135] The fibers used in making the sheets and other articles of thepresent invention preferably have a high length to width ratio (or“aspect ratio”) because longer, narrower fibers can impart more strengthto the polymer blend while adding significantly less bulk and mass tothe matrix than thicker fibers. The fibers will have an aspect ratio ofat least about 10:1, preferably greater than about 25:1, more preferablygreater than about 50:1, and most preferably greater than about 100:1.

[0136] The amount of fibers added to the polymer blends will varydepending upon the desired properties of the finished article ofmanufacture, with tensile strength, toughness, flexibility, and costbeing the principle criteria for determining the amount of fiber to beadded in any mix design. Accordingly, the concentration of fibers withinthe polymer blends of the present invention can be included in a broadrange from 0% to about 90% by weight of the polymer blend. If includedat all, fibers will preferably be included in an amount in a range fromabout 1% to about 80% by weight of the polymer blend, more preferably ina range from about 3% to about 50% by weight, and most preferably in arange from about 5% to about 30% by weight of the polymer blend.

[0137] C. Organic Fillers

[0138] The polymer blends may also include a wide range of organicfillers. Depending on the melting points of the polymer blend andorganic filler being added, the organic filler may remain as a discreteparticle and constitute a solid phase separate from the thermoplasticphase, or it may partially or wholly melt and become partially or whollyassociated with the thermoplastic phase.

[0139] Organic fillers may comprise a wide variety of natural occurringorganic fillers such as, for example, seagel, cork, seeds, gelatins,wood flour, saw dust, milled polymeric materials, agar-based materials,native starch granules, pregelatinized and dried starch, expandableparticles, and the like. Organic fillers may also include one or moresynthetic polymers of which there is virtually endless variety. Becauseof the diverse nature of organic fillers, there will not generally be apreferred concentration range for the optional organic filler component.

[0140] Organic fillers can partially or wholly take the place ofinorganic fillers. In some cases, organic fillers can be selected thatwill impart the same properties as inorganic fillers, such as toincrease dead-fold, the bulk hand feel, breathability and water vaportransmission. When included at all, the organic filler component willtypically be included in an amount of at least about 5% by weight of theoverall composition, preferably at least about 10% by weight, morepreferably at least about 20% by weight, and more especially preferablyat least about 30% by weight, and most preferably at least about 35% byweight of the overall composition.

[0141] 3. Natural Polymers.

[0142] In addition to thermoplastic starch or starch particles, othernatural polymers that may be used within the polymer blends comprise orare derivatives of cellulose, other polysaccharides, polysaccharide gumsand proteins.

[0143] Examples of starches and starch derivatives include, but are notlimited to, modified starches, cationic and anionic starches, and starchesters such as starch acetate, starch hydroxyethyl ether, alkylstarches, dextrins, amine starches, phosphates starches, and dialdehydestarches.

[0144] Examples of derivatives of cellulose include, but are not limitedto, cellulosic esters (e.g., cellulose formate, cellulose acetate,cellulose diacetate, cellulose propionate, cellulose butyrate, cellulosevalerate, mixed esters, and mixtures thereof) and cellulosic ethers(e.g., methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose, and mixturesthereof).

[0145] Other polysaccharide-based polymers that can be incorporated intothe polymer blends of the invention include alginic acid, alginates,phycocolloids, agar, gum arabic, guar gum, acacia gum, carrageenan gum,furcellaran gum, ghatti gum, psyllium gum, quince gum, tamarind gum,locust bean gum, gum karaya, xanthan gum, and gum tragacanth, andmixtures or derivatives thereof.

[0146] Suitable protein-based polymers include, for example, Zein® (aprolamine derived from corn), collagen (extracted from animal connectivetissue and bones) and derivatives thereof such as gelatin and glue,casein (the principle protein in cow milk), sunflower protein, eggprotein, soybean protein, vegetable gelatins, gluten and mixtures orderivatives thereof.

[0147] b 4. Non Biodegradable Polymers.

[0148] Although polymer blends preferably include biodegradablepolymers, it is certainly within the scope of the invention to includeone or more polymers which are not biodegradable. If thenonbiodegradable polymer generally comprises a disperse phase ratherthan the dominant continuous phase, polymer blends that include anonbiodegradable polymer will nevertheless be biodegradable, at least inpart. When degraded, the polymer blend may leave behind anonbiodegradable residue that nevertheless is superior to the waste leftbehind by sheets and films that are entirely made of nonbiodegradablepolymers.

[0149] Examples of common nonbiodegradable polymers suitable for formingsheets and films include, but are not limited to, polyethylene,polypropylene, polybutylene, PET, PETG, PETE, polyvinyl chloride, PVDC,polystyrene, polyamides, nylon, polycarbonates, polysulfides,polysulfones, copolymers including one or more of the foregoing, and thelike.

[0150] D. Polymer Blends.

[0151] 1. Concentration Ranges of Biodegradable Polymers.

[0152] The concentrations of the various components within the polymerblends used to treat fibrous sheets will depend on a number of factors,including the desired physical and mechanical properties of the treatedsheet, the performance criteria of articles to be manufactured from atreated sheet, the processing equipment used to manufacture and convertthe blends and treated sheets into the desired article of manufacture,and the particular components within the blends. One of ordinary skillin the art will be able, in light of the specific examples and otherteachings disclosed herein, to select and optimize the concentrations ofthe various components through routine testing.

[0153] In view of the wide variety of polymer blends within the scope ofthe invention, as well as the wide variety of different properties thatmay be engineered within the blends, the hard and soft polymers may beincluded within widely varying concentration ranges. In those caseswhere the polymer blend or composition includes a blend of stiff andsoft biodegradable polymers, the one or more stiff biodegradablepolymers within the inventive blends may have a concentration in a rangefrom about 20% to about 99% by weight of the biodegradable polymersexclusive of the fibrous sheet and any fillers, preferably aconcentration of at least about 30% by weight of the polymer blend, morepreferably at least about 40% by weight of the polymer blend, moreespecially preferably greater than, but not including, 50% by weight ofthe polymer blend, and most preferably at least about 55% by weight ofthe polymer blend.

[0154] Similarly, when a blend of stiff and soft polymers is employed,the soft polymers may have a concentration in a range from about 1% toabout 80% by weight of the biodegradable polymers exclusive of thefibrous sheet and any fillers, preferably a concentration up to about70% by weight of the polymer blend, more preferably up to about 60% byweight of the polymer blend, more especially preferably less than, butnot including, 50% by weight of the polymer blend, and most preferablyup to about 45% by weight of the polymer blend.

[0155] The foregoing concentrations are measured in terms of the blendof hard and soft polymers exclusive of any optional components that maybe added, as described and identified above.

[0156] 2. Properties of Polymer Blends and Treated Sheets.

[0157] The polymer blends may be engineered to have a variety of desiredproperties as described herein. The properties of the final treatedfibrous sheet will depend on a number of factors, including mix designof the polymer blend, processing conditions, post-formation processing,product size, particularly thickness, and the like. In the case oftreated sheets intended to be used as “wraps”, such as wraps used toenclose meats, other perishable food items, and especially fast fooditems (e.g., sandwiches, burgers and dessert items), it will generallybe desirable to provide treated sheets having good “dead-fold”properties so that once folded, wrapped or otherwise manipulated into adesired orientation, such wraps will tend to maintain their orientationso as to not spontaneously unfold or unwrap, as which occurs with alarge number of plastic sheets and films (e.g., polyethylene).

[0158] In order to improve the dead-fold properties of treated sheetsbiodegradable polymers may be selected which yield blends having arelatively high Young's modulus, preferably at least about 100 MPa, morepreferably at least about 150 MPa, and most preferably at least about200 MPa. In general, increasing the concentration of the stiffbiodegradable polymer will tend to increase the Young's modulus. TheYoung's modulus may also be increased by loading the polymer blends withone or more fillers, such as particulate or fibrous fillers, asdescribed above.

[0159] In addition to, or instead of, increasing the Young's modulus toimprove dead-fold, the treated sheets may be optionally processed toincrease the “bulk hand feel” of a sheet, which is done by disruptingthe generally planar nature of the sheet. This can be done, for example,by embossing, crimping, quilting or otherwise texturing the sheet so asto have regularly spaced-apart or random hills and valleys rather thansimply a smooth, planar sheet. This may be done, for example, by passingthe sheet through a pair of knurled or other embossing-type rollers.Such texturing increases the ability of a sheet to take and maintain afold, crinkle, creases or other bend, thus improving the dead-foldproperties of the sheet.

[0160] Another way to increase the surface area of the treated sheetsaccording to the invention so as to increase their bulk hand feel and/ordead-fold is to include particulate fillers in which at least a portionof the particles have a particle size diameter that equals or exceedsthe thickness of the polymer coating. In this way, treated sheets can bemanufactured that have dead-fold approaching or equaling 100%, whichexceeds the dead-fold properties of virtually all conventional paper orplastic wraps and sheets currently on the market. An example of aconventional sheet or wrap having 100% dead-fold is aluminum or othermetal foils.

[0161] Other properties that may be desirable when manufacturing foodwraps are heat resistance, microwaveability, and insulation ability.Increasing the amount of inorganic filler within the polymer blend orcomposition used to coat or impregnate a fibrous sheet tends to increasethe heat resistance, microwaveability, and insulation ability of thetreated fibrous sheets. It has been found, for example, that a softbiodegradable polymer can be blended with an inorganic filler, such asground or precipitated silica, to yield a biodegradable polymercomposition that includes at least about 30% by weight of the inorganicfiller. Adding at least about 30% by weight inorganic filler to a softbiodegradable polymer yields a treated fibrous sheet that does not breakdown when placed in a microwave oven.

[0162] The use of fillers, coupled with specific processing techniques,can also be used to create “cavitation”. Cavitation occurs as thethermoplastic polymer fraction is pulled in either a monoaxial orbiaxial direction and the filler particles create a discontinuity in thefilm or sheet that increases in size during stretching. Duringstretching, a portion of the stretched polymer pulls away from thefiller particles, resulting in tiny cavities in the vicinity of thefiller particles. This, in turn, results in greatly increasedbreathability and vapor transmission of the sheets and films. It alsoresults in films or sheets having a touch and feel that much moreclosely resembles the touch and feel of paper, as contrasted withconventional plastic sheets and films. The result is a sheet, film orwrap that can be used for applications that are presently performed orsatisfied using paper products (i.e., wraps, tissues, printed materials,etc.)

[0163] Treated sheets according to the invention can have any desiredthickness. Treated sheets suitable for wrapping, enclosing or otherwisecovering food items or other solid substrates will typically have ameasured thickness between about 0.0003″ and about 0.01″ (about 7.5-250microns), and a calculated thickness between about 0.00015″ and about0.005″ (about 4-125 microns).

[0164] The measured thickness will typically be between 10-100% largerthan the calculated thickness when the sheets and films are made fromcompositions that have a relatively high concentration of particulatefiller particles, which can protrude from the surface of the treatedsheet. This phenomenon is especially pronounced when significantquantities of filler particles having a particle size diameter that islarger than the thickness of the polymer matrix are used.

[0165] Treated sheets suitable for use as wraps will preferably have ameasured thickness in a range from about 0.0004″ to about 0.005″ (about10 to about 125 microns), more preferably in a range from about 0.0005″to about 0.003″ (about 12 to about 75 microns), and most preferably in arange from about 0.001″ to about 0.002″ (about 25 to about 50 microns).On the other hand, treated sheets suitable for use as wraps willpreferably have a calculated thickness in a range from about 0.0002″ toabout 0.003″ (about 5 to about 75 microns), more preferably in a rangefrom about 0.0003″ to about 0.002″ (about 7.5 to about 50 microns), andmost preferably in a range from about 0.0005″ to about 0.0015″ (about 12to about 40 microns).

[0166] The difference between the calculated and measured thicknesstends to increase with increasing filler content and also withincreasing particle size. Conversely, the difference between thecalculated and measured thickness tends to decrease with decreasingfiller content and also with decreasing particle size. Treated sheetsthat include no fillers, or lower quantities of fillers having aparticle size diameter that is substantially lower than the thickness ofthe polymer matrix, will have a measured thickness that is similar orequal to the calculated thickness.

[0167] Another important property of the biodegradable blends is thatwhen such blends are used to coat or impregnate fibrous sheets, thetreated sheets are readily printable without further processing. Thus,another advantage of utilizing the inventive polymer blends in themanufacture of wraps is that such blends are generally able to acceptand retain print much more easily than conventional plastics or waxedpapers. Many plastics and waxes are highly hydrophobic and must besurface oxidized in order to provide a chemically receptive surface towhich ink can adhere. Biodegradable polymers, on the other hand,typically include oxygen-containing moieties, such as ester or amidegroups, to which inks can readily adhere.

[0168] 3. Measuring Dead-Fold

[0169] The term “dead-fold” refers to the tendency of a sheet tomaintain a crease, crinkle, fold or other bend. The dead-fold propertiesof a sheet can be accurately measured using a standard test known in theart. This test provides the ability to compare and contrast thedead-fold properties of various sheets. The following equipment isuseful in performing the standard dead-fold test: (1) a semicircularprotractor, divided along a 1″ diameter semicircle; (2) a weightconsisting of a smooth-faced metal block that is 0.75″±0.05″ by1.25″±0.05″ and of such a thickness so as to weigh 50 g±0.05 g; (3) a1″×4″ template for cutting test specimens; (4) a timer or stopwatchcapable of timing to 1 second; (5) a utility knife or other cuttingtool; and (6) a humidity chamber.

[0170] The first step is preparation of an appropriately sized sample.In the case where a sheet has different properties in the machinedirection compared to the cross-machine direction it may be useful tomeasure and average the dead-fold properties in both directions. Thestandard sample specimen is a 1″×4″ strip of the sheet to be tested.

[0171] The second step is a conditioning step in order to ensureuniformity of test conditions. The specimens are conditioned by placingthem in a humidity chamber at 23 C and 50% relative humidity for aminimum of 24 hours.

[0172] The third step is the actual dead-fold test of each conditionedtest strip. The specimen is removed from the humidity chamber and itsweight recorded. A light mark is made 1″ from one end of the test strip.The test strip is then placed on a flat surface and bent over at themark but without creasing the strip. Next, the weight is placed squarelyand gently over the bend with two thirds (or 0.5″) of the weightoverlapping the specimen so that a crease is formed, and with one thirdor (0.25″) of the weight overhanging the crease. The edges of the weightparallel to the strip should project evenly (about 0.125″) beyond eachside of the strip. The weight is allowed to rest on the specimen for 10seconds. Then it is removed. After exactly 30 seconds, the angle formedby the crease is measured.

[0173] The foregoing process is repeated using the other side of thestrip and using as many additional strips as will give a statisticallyaccurate measure of the dead-fold properties of a given sheet or film.The average angle A is then input into the following formula todetermine the percentage dead-fold C for a given sample:

C=100*(180-A)/180

[0174] If the angle A is 0° (i.e., where the crease is maintained sothat no spring back is observed), the sample has 100% dead-fold(C=100*(180-0)/180=100%). At the other extreme, if the angle A is 180°(i.e., where the sample springs all the way back so that the sample isessentially flat, the sample has 0% dead-fold (C=100*(180-180)/180=0%).In the middle, a sample that springs back half way so as to form a rightangle has 50% dead-fold (C=100*(180-90)/180=50%).

[0175] When used to wrap foods, or whenever good dead-fold propertiesare desired, treated sheets according to the invention can bemanufactured so as to have a dead-fold of at least about 50%.Preferably, treated sheets will have a dead-fold of at least about 60%,more preferably at least about 70%, more especially preferably at leastabout 80%, and most preferably at least about 90%. Treated sheetsaccording to the invention have been developed that have a dead-foldapproaching or equal to 100%. By way of comparison, sheets and filmsmade from polyethylene (e.g., for use in making sandwich or garbagebags) typically have a dead-fold of 0%. Standard paper wraps commonlyused in the fast food industry typically have a dead-fold between about40-80%. Thus, treated sheets according to the invention can bemanufactured so as to have dead-fold properties that meet or exceedthose of standard paper wraps, and which are many times greater thanconventional plastic films and sheets, often orders of magnitudegreater.

[0176] III. Methods of Manufacturing Polymer Blends and Fibrous Sheets

[0177] It is within the scope of the invention to employ anymanufacturing apparatus known in the art of manufacturing thermoplasticcompositions to form the polymer and any coating apparatus to coat orimpregnate fibrous sheets with the polymer blends. Examples of suitablemixing apparatus that can be used to form polymer blends accordinginclude a twin-shafted kneader with meshing screws having kneadingblocks sold by the Buss Company, a BRABENDER mixer, a THEYSOHN TSK 045compounder, which is a twin-shaft extruder with shafts rotating in thesame direction and which has multiple heating and processing zones, aBUSS KO Kneader having a heatable auger screw, a BAKER-PERKINS MPC/V-30double and single auger extruder, single or twin auger OMC extruders, aModel EPV 60/36D extruder, a BATTAGGION ME100 direct-current slow mixer,a HAAKE Reomex extruder, a COLLIN Blown Film Extruder, aBATTENFELD-GLOUCESTER Blown Film Extruder, and a BLACK-CLAWSON Cast FilmExtruder.

[0178] Many of the foregoing mixers are also extruders, which makes themsuitable for extruding films or sheets from the polymer blends, whichcan then be laminated together with a fibrous sheet. Alternatively,polymer blends can be made using transfer-line-injection technologywhere resin manufacturers can inject the various minor components ofthese blends into the main poly components during manufacture. One ofordinary skill in the art will be able to select and optimize anappropriate manufacturing apparatus according to the desired article tobe manufactured. Once a thermoplastic melt has been formed using any ofthe above-mentioned mixers, or any other appropriate mixing and meltingapparatus known in the thermoplastic art, virtually any molding,extrusion, shaping or coating apparatus known in the thermoplasticmolding or processing art can be used to produce finished articles ofmanufacture comprising fibrous sheets that have been coated orimpregnated with a polymer blend to render the sheets more resistant topenetration by liquids.

[0179] In a preferred embodiment for manufacturing sheets and films fromthe polymer blends, which can then be laminated together with fibroussheets, the sheets and films can be manufactured using a compoundingtwin screw extruder to prepare the blends, and a blown film or cast filmline to make the films and sheets. Blown films and sheets tend to havesimilar, if not identical, strength and other performance properties inthe biaxial direction due to how they are processed (i.e., they areextruded as a tube and then expanded in all directions by blowing airwithin the confines of the tube, causing it to expand like a balloon).Cast films or sheets, on the other hand, unless subjected to biaxialstretching, will be substantially stronger (e.g. will have substantiallygreater tensile strength) in the machine direction and will besubstantially more tear resistant in the cross-machine direction. Whenextruding a thermoplastic material, the polymer molecules tend to beoriented in the machine direction. Machine direction orientation isfurther increased if the extruded sheet or film is passed through a nipto decrease the sheet or film thickness in the machine direction.

[0180] The treated sheets according to the invention may be coated orimpregnated on one or both sides as desired. They may be formed bylaminating a fibrous sheet with one or more sheets or films,co-extruding a sheet or film of a polymer blend with a fibrous sheet,dipping, spreading (e.g., using a doctor blade), spraying, and the like.Because a portion of the treated sheets are thermoplastic, the sheetscan be post-treated by heat sealing to join two ends together to formsacks, pockets, pouches, and the like. They can be laminated ontoexisting sheets or substrates.

[0181] Monoaxial or biaxial stretching of sheets and films used to coata surface of a fibrous sheet can be used to create cavitation. To createcavitation, a particulate filler is included that yields discontinuitiesas the sheet or film is stretched while still in a thermoplasticcondition. Cavitation increases the breathability and vapor transmissionof the sheets and films. It also results in films or sheets having atouch and feel that much more closely resembles the touch and feel ofpaper compared to conventional thermoplastic sheets and films.

[0182] When employing certain coating or impregnating techniques, suchas spreading or spraying a biodegradable polymer composition onto afibrous sheet, it may be advantageous to increase the MFI of the moltenpolymer composition. This allows the molten polymer composition to flowmore readily so as to coat or impregnate the fibrous sheet. Preferably,the molten polymer composition has an MFI of at least about 40 g/10min., more preferably at least about 70 g/10 min., and most preferablyat least about 100 g/10 min.

[0183] As discussed above, the MFI can, depending on the biodegradablepolymer or polymer blend, be increased to a desired level by heating itto a higher temperature. In some cases, however, heating a polymer totemperature that might theoretically decrease the MFI to an acceptablelevel might, instead, scorch, bum or otherwise damage the polymercomposition. In such cases it may be desirable to add a plasticizer tothe polymer composition. The plasticizer might be a volatile ornon-volatile plasticizer, as discussed above.

[0184] According to one embodiment, water is added to increase the MFIof the molten polymer composition. Adding 200 ppm water to a polymercomposition has been found to increase the MFI from 4 g/10 min. to 40g/10 min. Based on this, one of ordinary skill can adjust the waterconcentration as desired to raise or lower the MFI to a predeterminedlevel.

[0185] In the case of a spray coating method, one or more volatilesolvents, such as alcohols, ketones, or chlorinated hydrocarbons, can beused to raise the MFI of the molten polymer composition. During or afterthe coating process, as the volatile solvent is driven off byevaporation, the solvent is advantageously recovered and reused for botheconomic and environmental reasons.

IV. Examples

[0186] The following examples are presented in order to morespecifically teach compositions and process conditions for formingbiodegradable polymer blends, as well as treated fibrous sheetstherefrom. The examples include various mix designs of the degradablepolymer blends as well various processes for manufacturing the enforming polymeric sheets and films therefrom.

Examples 1-3

[0187] Biodegradable polymer films were manufactured from biodegradablepolymer blends having the following mix designs, with the concentrationsbeing expressed in terms of weight percent of the entire polymer blend:Example Biomax 6926 Ecoflex-F SiO₂ 1 94.84%  5% 0.16% 2 89.84% 10% 0.16%3 79.84% 20% 0.16%

[0188] The foregoing polymer blends were blended and blown into films atGemini Plastics, located in Maywood, Calif., using DuPont suppliedBIOMAX 6926 (both new and old lots), a silica master batch in BIOMAX6926 base resin supplied by DuPont, and ECOFLEX-F resin obtained fromBASF. The films were blown using a Gemini film blowing extruder (L/D24/1) equipped with a 2 inch barrier mixing screw containing a Maddockshear mixing tip, and a 4 inch diameter annular die with a die gap of0.032-0.035″.

[0189] Even though a typical quantity of silica antiblock was used(i.e., 0.16%), significant blocking of the film was observed for thefilm made using the mix design of Example 3 (i.e. 20% ECOFLEX); however,there was no observed blocking of the 5 and 10% ECOFLEX blends ofExamples 1 and 2. For purposes of comparison, films of neat ECOFLEX andBIOMAX were manufactured. The neat ECOFLEX films were manufactured usingBASF ECOFLEX-F resin and a 30% talc master batch in the same resin. Theneat BIOMAX films (new and old) included 0.16% SiO₂, while the neatECOFLEX films included 4.5% talc. The mechanical properties of theBIOMAX/ECOFLEX blend films and the control BIOMAX and neat ECOFLEX-Ffilms were measured under ambient conditions. The data generated is showgraphically in Charts 1-8 depicted in FIGS. 1-8, respectively.

[0190] Chart 1, depicted in FIG. 1, is a plot of the strain rate versuspercent elongation at break for the various films tested. At 500 mm/min.strain rate, both new and old BIOMAX films displayed poor elongation.The neat ECOFLEX films and all of the films made from the BIOMAX-ECOFLEXblends had significantly better elongations than the neat BIOMAX filmsat all of the strain rates studied. On the other hand, the 20% ECOFLEXblend of Example 3 exhibited equal or better elongation compared to theneat ECOFLEX films at lower strain rates, even though these filmsincluded nearly 80% BIOMAX, which was shown to have very poorelongation.

[0191] Chart 2, depicted in FIG. 2, is a plot of percent elongationversus percentage of ECOFLEX in the BIOMAX/ECOFLEX blends measured at afixed strain rate of 500 mm/min. As represented by Chart 2, there was anearly linear improvement in the percent elongation as the concentrationof ECOFLEX was increased. Moreover, the 20% ECOFLEX blend of Example 3had an elongation as good as the neat ECOFLEX films.

[0192] Chart 3, depicted in FIG. 3, similarly plots the percentelongation versus the percentage of ECOFLEX in the BIOMAX/ECOFLEX blendsmeasured at a fixed strain rate of 1000 mm/min. Again, a dramaticimprovement in the elongation of the BIOMAX/ECOFLEX blend was seen asthe concentration of ECOFLEX reached 10 and 20%, respectively, althoughthe trend was not as clear as the data in Chart 2, measured at a fixedstrain rate of 500 mm/min.

[0193] Chart 4, depicted in FIG. 4, is a plot of the strain rate versusbreak stress of the various films. Again, neat ECOFLEX and all of theBIOMAX/ECOFLEX blends had significantly better break stress than theneat BIOMAX films at all of the strain rates studied. Moreover, theBIOMAX/ECOFLEX blends had significantly better break stress than theneat ECOFLEX films at all strain rates, thus showing that theBIOMAX/ECOFLEX blends are all stronger in tensile strength than eitherof neat BIOMAX or ECOFLEX.

[0194] Chart 5, depicted in FIG. 5, is a plot of the break stress versuspercent ECOFLEX in the BIOMAX/ECOFLEX blends of Examples 1-3 measured ata fixed strain rate of 500 mm/min. Once again, a nearly linear increasein break stress was observed as the concentration of ECOFLEX wasincreased. Moreover, the 20% blend of Example 3 exhibited the surprisingand unexpected result of having nearly twice the break stress as theneat ECOFLEX film, and nearly three times the break stress as the neatBIOMAX film.

[0195] Chart 6, depicted in FIG. 6, is a plot of the break stress versuspercent ECOFLEX in the BIOMAX/ECOFLEX blends of Examples 1-3 measured ata fixed strain rate of 1000 mm/min. At this strain rate, the 10% ECOFLEXblend of Example 2 had the highest break stress, with a maximum peakstress of 72 MPa.

[0196] Charts 7 and 8, depicted in FIGS. 7 and 8, respectively, plot thewater vapor permeability coefficient (WVPC) of the various films as afunction of the concentration of ECOFLEX within the films. In Chart 7,the estimated trend line is based on a WVPC of 7.79×10⁻³ g cm/m²/d/mmHg, which is the lowest measured WVPC for a neat ECOFLEX film. In Chart8, the estimated trend line is alternatively based on a WVPC of 42×10⁻³g cm/m²/d/mm Hg, which is the highest measured WVPC for a neat ECOFLEXfilm. The data in Charts 7 and 8 indicate that the water vapor barrierproperties of the 5 and 10% ECOFLEX blends of Examples 1 and 2 wereessentially the same as that of the neat BIOMAX film. The WVPC data forall samples were measured by the standard procedures described in theTest Method ASTM F 1249-90.

[0197] Chart 9, depicted in FIG. 9, is a plot of the modulus of variousfilms as a function of the concentration of ECOFLEX within the films.Surprisingly, the modulus of blends containing BIOMAX and ECOFLEX aresignificantly higher than of neat BIOMAX and ECOFLEX. Because one of theuses of the films manufactured according to the present invention is asa wrap having good dead-fold properties, and because the degree ofdead-fold is believed to be related to the modulus of a film, blends ofBIOMAX and ECOFLEX appear to have superior dead-fold properties overeach of the neat BIOMAX and ECOFLEX films, with the 5% and 10% blendsexhibiting the highest modulus.

[0198] The foregoing films are used to laminate at least one side of afibrous sheet, such as a tissue paper, more particularly a 12-15 lb/3000ft² tissue paper, to yield a treated sheet. The treated sheet can beused as a food packaging wrap that resists penetration by water and oilsfound in food.

Examples 4-5

[0199] Films were manufactured from biodegradable polymer blends havingthe following mix designs, with the concentrations being expressed interms of weight percent of the entire polymer blends: Example Biomax6926 Ecoflex-F Talc 4 79.7% 16.7% 3.6% 5 76.7% 16.7% 6.6%

[0200] The films were blown using a Gemini film blowing extruder (L/D24/1) equipped with a 2 inch barrier mixing screw containing a Maddockshear mixing tip, and a 4 inch diameter annular die with a die gap of0.032-0.035″. The film of Example 5 had better dead-fold properties thanthe film of Example 4, which might be attributable to the higherconcentration of talc within the blend used in Example 5.

[0201] The foregoing films are used to laminate at least one side of afibrous sheet, such as a tissue paper, more particularly a 12-15 lb/3000ft² tissue paper, to yield a treated sheet. The treated sheet can beused as a food packaging wrap that resist penetration by water and oilsfound in food.

Example 6

[0202] A film was manufactured from a biodegradable polymer blend havingthe following mix design, with the concentration being expressed interms of weight percent of the entire polymer blend: ECOFLEX-F 20%Thermoplastic Starch 50% Polylactic Acid 15% Inorganic Filler 15%

[0203] The Thermoplastic Starch was obtained from Biotec BiologischeNatuverpackungen GmbH & Co., KG (“Biotec”), located in Emmerich,Germany. The polylactic acid was obtained from Cargill-Dow Polymers,LLC, located in Midland, Mich., USA. The inorganic filler was calciumcarbonate obtained from OMYA, division Pluess-Staufer AG, located inOftringen, Switzerland.

[0204] The foregoing blend was manufactured and blown into films using aproprietary extrusion line thermoplastic starch extrusion/film blowingapparatus manufactured and assembled specifically for Biotec. Inparticular, the extrusion/film blowing apparatus was manufactured by Dr.Collin GmbH, located in Ebersberg, Germany. A detailed description of anextrusion/film blowing apparatus similar to the one used by Biotec isset forth in U.S. Pat. No. 5,525,281 to Lörcks et al. U.S. Pat. No.6,136,097 to Lörcks et al. discloses processes for manufacturingintermediate thermoplastic starch-containing granulates that can befurther processed to make films and sheets. For purposes of disclosure,the foregoing patents are incorporated herein by reference.

[0205] The film had a modulus of 215.65 MPa. Thus, it had excellentdead-fold properties as a result of the inclusion of the inorganicfiller and the polylactic acid, which is a generally stiff, crystallinepolymer at room temperature. As set forth above, has a glass transitiontemperature between 50-60° C. The ECOFLEX and thermoplastic starch (TPS)both acted as soft, low glass transition temperature polymers. The TPS,when blended with additional polymers and at very low water, has a glasstransition temperature approaching −60° C. The ECOFLEX and TPS thusassisted the blowability and flexibility of the blend. The TPS alsoincreased the natural polymer content, thus making the film morebiodegradable.

[0206] The foregoing film is used to laminate at least one side of afibrous sheet, such as a tissue paper, more particularly a 12-15 lb/3000ft² tissue paper, to yield a treated sheet. The treated sheet can beused as a food packaging wrap that resists penetration by water and oilsfound in food.

Example 7

[0207] A film was manufactured from a biodegradable polymer blend havingthe following mix design, with the concentration being expressed interms of weight percent of the entire polymer blend: ThermoplasticStarch 30% BAK 1095 60% Inorganic Filler 10%

[0208] The thermoplastic starch was obtained from Biotec. The BAK 1095was obtained from Bayer AG, located in Köln, Germany, and was analiphatic-aromatic polyesteramide. The inorganic filler was calciumcarbonate obtained from OMYA, division Pluess-Staufer AG, located inOftringen, Switzerland.

[0209] The foregoing blend was manufactured and blown into films usingthe proprietary thermoplastic starch extrusion/film blowing apparatusdescribed in Example 6. The film had excellent dead-fold properties as aresult of the inclusion of the inorganic filler and the BAK 1095, whichis a somewhat stiff, crystalline polymer at room temperature even thoughit is classified as “film grade”. As set forth above, BAK 1095 behavesas if it has a glass transition temperature of at least 10C. Because theglass transition temperature of BAK 1095 is relatively low compared toPLA, considerably more BAK could be included without destroying thefilm-blowing properties and flexibility of the resulting film. The TPSacted as the soft, low glass transition temperature polymer, and furtherassisted the blowability and flexibility of the blend. It also increasedthe natural polymer content, thus making the film more biodegradable.

[0210] The foregoing film is used to laminate at least one side of afibrous sheet, such as a tissue paper, more particularly a 12-15 lb/3000ft² tissue paper, to yield a treated sheet. The treated sheet can beused as a food packaging wrap that resists penetration by water and oilsfound in food.

Examples 8-12

[0211] Films were manufactured from biodegradable polymer blends havingthe following mix designs, with the concentrations being expressed interm of weight percent of the entire polymer blend: Example Biomax 6926Ecoflex F Talc TiO₂ CaCO₃  8   76%   15% 4.5% 4.5% —  9 85.5%  9.5% —  5% — 10   70% 17.5% — 2.5% 10% 11   66% 16.5% — 2.5% 15% 12   58%  24% —   3% 15%

[0212] The talc was supplied by Luzenac, located in Englewood, Colo.,having a particle size of 3.8 microns. The titanium dioxide was suppliedby Kerr-McGee Chemical, LLC, located in Oklahoma City, Okla., gradeTRONOX 470, having a particle size of 0.17 micron. The calcium carbonatewas supplied by Omnia, located in Lucerne Valley, Calif., particle sizeof 2 microns. The foregoing blends were manufactured on a WernerPfeiderer ZSK twin-screw extruder, and blown into sheets using a Geminifilm blowing extruder (L/D 24/1) equipped with a 2 inch barrier mixingscrew containing a Maddock shear mixing tip, and a 4 inch diameter die.All of the films had excellent dead-fold properties. The polymer blendsof Examples 10-12 were also extruded into sheets using a single screwextruder and a 14 inch flat cast-film die, and the usual nip-rolls andfilm take-up assembly normal to such a system. All of these films alsohad excellent dead-fold properties.

[0213] The foregoing films are used to laminate at least one side of afibrous sheet, such as a tissue paper, more particularly a 12-15 lb/3000ft² tissue paper, to yield a treated sheet. The treated sheet can beused as a food packaging wrap that resists penetration by water and oilsfound in food.

Examples 13-61

[0214] Blown and cast films and sheets were manufactured frombiodegradable polymer blends having the following mix designs, with theconcentrations being expressed in term of weight percent of the entirepolymer blend: Ecoflex Eastar Bio Eastar Bio Example PLA Biomax BX 7000Ultra GP CaCO₃ TiO₂ Starch 13 30% 0% 45% 0%  8.25%  14.5%  2.25%   0% 1430% 0% 30% 0%  13.2%  23.2%  3.6%   0% 15 30% 0% 25% 0% 11.55%  20.3%3.15%   10% 16 50% 0% 25% 0%  8.25%  14.5% 2.25%   0% 17 50% 0% 10% 0% 13.2%  23.2%  3.6%   0% 18 50% 0%  5% 0% 11.55%  20.3% 3.15%   10% 1950% 0%  0% 0%  16.5%  29.0%  4.5%   0% 20 50% 0%  0% 0%  13.2%  23.2% 3.6%   10% 21 50% 0%  0% 0% 11.55%  20.3%  3.2%   15% 22 50% 0%  0% 0% 9.9%  17.4%  2.7%   20% 23 50% 0%  0% 0%  8.25%  14.5% 2.25%   25% 2427% 0% 64% 0%  2.97%  5.22% 0.81%   0% 25 25% 0% 58% 0%  5.61%  9.86%1.53%   0% 26 23% 0% 54% 0%  7.59% 13.34% 2.07%   0% 27 30% 0% 40% 0%   0%  0.0%  0.0%   30% 28 15% 0% 60% 0%    0%  0.0%  0.0%   25% 29 25%0% 25% 0%  16.5%  29.0%  4.5%   0% 30 20% 0% 20% 0%  19.8%  34.8%  5.4%  0% 31 35% 0%  5% 0%  19.8%  34.8%  5.4%   0% 32 40% 0% 10% 0%  16.5% 29.0%  4.5%   0% 33 50% 0%  0% 0%  16.5%  29.0%  4.5%   0% 34 20% 0% 0% 20%   19.8% 34.8%  5.4%   0% 35 27% 0% 36% 0%  3.3%  5.8%  0.9%  27% 36 21% 0% 28% 0%  9.9%  17.4%  2.7%   21% 37 28.5%   0% 38% 5%   0%    0%   0% 28.5% 38 40% 0%  0% 7%  16.5%  29.0%  4.5%   3% 39 40%0%  7% 0%  16.5%  29.0%  4.5%   3% 40 50% 0%  0% 0%  16.5%  29.0%  4.5%  0% 41 20% 0%  0% 20%   19.8%  34.8%  5.4%   0% 42 30% 0%  0% 14%  16.5%  29.0%  4.5%   6% 43 40% 0%  0% 14%   13.2%  23.2%  3.6%   6% 44 0% 40%   0% 14%   13.2%  23.2%  3.6%   6% 45  0% 50%   0% 0%  16.5% 29.0%  4.5%   0% 46  0% 45%   0% 0% 18.15%  31.9% 4.95%   0% 47  0%40%   0% 0%  19.8%  34.8%  5.4%   0% 48  0% 40%   0% 0%  19.8%  34.8% 5.4%   0% 49 40% 0% 14% 0%  13.2%  23.2%  3.6%   6% 50  0% 30%   0% 7% 19.8%  34.8%  5.4%   3% 51  0% 35%   0% 7% 18.15%  31.9% 4.95%   3% 52 0% 38%   0% 1.4%    19.8%  34.8%  5.4%  0.6% 53  0% 35%   0% 3.5%   19.8%  34.8%  5.4%  1.5% 54 40% 0%  0% 14%   13.2%  23.2%  3.6%   6% 5540% 0%  0% 0%  26.7%  22.7%  3.5%  7.1% 56 40% 0%  0% 13.8%    12.9% 22.7%  3.5%  7.1% 57 40% 0%  0% 26.7%      0%  22.7%  3.5%  7.1% 58 40%0%  0% 13.8%    12.9%  22.7%  3.5%  7.1% 59 40% 0%  0% 0%  26.7%  22.7% 3.5%  7.1% 60 40% 0%  0% 14%   13.2%  23.2%  3.6%   6% 61  0% 50%   0%0%  16.5%  29.0%  4.5%   0%

[0215] The compositions of Examples 13-59 were all processed and blowninto films using a COLLIN Blown Film Extruder. The films made using thecompositions of Examples 30-34, 36, 38, 41 and 43 were tested and foundto have dead-folds of 100%, 92%, 91%, 100%, 100%, 100%, 100% and 100%,respectively. Although films made from the other compositions were nottested for dead-fold, they would be expected to have relatively highdead-fold compared to conventional biopolymers (i.e., at least about80%). The water vapor transmission rate for films made using thecompositions of Examples 36, 38, 41 and 43 were 91.94, 91.32, 98.29 and80.31 g/m²/day, respectively.

[0216] The composition of Example 60 was processed and blown into a filmusing a BATTENFELD-GLOUCESTER Blown Film Extruder. A film made from thiscomposition was found to have a water vapor transmission rate of 42.48g/m²/day.

[0217] The composition of Example 61 was processed and blown intovarious films using both a BATTENFELD-GLOUCESTER Blown Film Extruder anda BLACK-CLAWSON Cast Film Extruder. The film formed using theBATTENFELD-GLOUCESTER Blown Film Extruder apparatus was tested and foundto have a dead-fold of 100%. Two different thicknesses of films wereformed using the BLACK-CLAWSON Cast Film Extruder, one having athickness of 1.3 mils (0.0013″) and another having a thickness of 1.8mils (0.0018″). Both had a distinctive machine direction orientationbecause they were cast, rather than blown, films. The 1.3 mil film had adead-fold of 99%, and the 1.8 mil film had a dead-fold of 100%.

[0218] The foregoing films and sheets are used to laminate at least oneside of a fibrous sheet, such as a tissue paper, more particularly a12-15 lb/3000 ft² tissue paper, to yield a treated film or sheet. Thetreated film or sheet can be used as a food packaging wrap that resistspenetration by water and oils found in food.

Example 62

[0219] Any of the foregoing biodegradable polymer blends is used to coator impregnate at least one side of a fibrous sheet. The polymer blend isheated, mixed or otherwise processed into a thermoplastic melt and thenspread over a surface of a fibrous sheet using a doctor blade. Thefibrous sheet is moved while the doctor blade remains stationary.Alternatively, the polymer blend is sprayed onto the fibrous sheet usingspray-coating techniques known in the art.

Example 63

[0220] Any of the foregoing biodegradable polymer blends is modified byadding silica or replacing some or all of the calcium carbonate withsilica. The modified composition is used to coat or impregnate at leastone side of a fibrous sheet. The polymer blend is heated, mixed orotherwise processed into a thermoplastic melt and then spread over asurface of a fibrous sheet using a doctor blade. The fibrous sheet ismoved while the doctor blade remains stationary. Alternatively, thepolymer blend is sprayed onto the fibrous sheet using spray-coatingtechniques known in the art.

Example 64

[0221] Any of the foregoing compositions is modified by removing atleast a portion of the particulate filler and then using the modifiedbiodegradable composition to coat one or both sides of a fibrous sheet.

[0222] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. An article of manufacture comprising: a fibrous sheet, atleast a portion of the fibrous sheet being coated or impregnated with abiodegradable composition that renders the fibrous sheet more resistantto liquids, the biodegradable composition comprising: at least one softthermoplastic biodegradable polymer having a glass transitiontemperature less than about 0° C.; and at least one stiff thermoplasticbiodegradable polymer having a glass transition temperature of at leastabout 10° C.
 2. An article of manufacture as defined in claim 1, whereinthe stiff thermoplastic biodegradable polymer comprises a modifiedpolyethylene terephthalate in which a portion of the terephthalategroups are substituted with at least one aliphatic diacid.
 3. An articleof manufacture as defined in claim 1, wherein the stiff thermoplasticbiodegradable polymer comprises at least one of a polyesteramide, apolyhydroxybutyrate having a glass transition temperature of at leastabout 10° C., a terpolymer including units formed from glycolide,lactide and ε-caprolactone, or a polyesteramide formed from at least onediacid, at least one diol, and at least one amino acid.
 4. An article ofmanufacture as defined in claim 1, wherein the stiff thermoplasticbiodegradable polymer comprises at least one of a polylactic acid or apolylactic acid derivative.
 5. An article of manufacture as defined inclaim 1, wherein the soft thermoplastic biodegradable polymer comprisesat least one of an aliphatic polyester including units formed from atleast one of a lactide or a hydroxyacid having at least 4 carbon atoms,a polyester including units formed from succinic acid and an aliphaticdiol, and at least one aliphatic diol, polycaprolactone,polyhydroxybutyrate-hydroxyvalerate copolymer, polybutylene succinate,polybutylene succinate adipate, polyethylene succinate, or thermoplasticstarch.
 6. An article of manufacture as defined in claim 1, wherein thesoft thermoplastic biodegradable polymer comprises at least one of analiphatic-aromatic copolyester including units formed from an aliphaticdiol, an aliphatic diacid and an aromatic diacid or analiphatic-aromatic copolyester including units formed from adipic acid,dialkyl terephthalate, and at least one aliphatic diol.
 7. An article ofmanufacture as defined in claim 1, wherein the stiff thermoplasticbiodegradable polymer is included in a range of about 20% to about 99%by weight of the biodegradable composition.
 8. An article of manufactureas defined in claim 1, wherein the stiff thermoplastic biodegradablepolymer is included in a concentration of at least about 40% by weightof the biodegradable composition.
 9. An article of manufacture asdefined in claim 1, wherein the stiff thermoplastic biodegradablepolymer is included in a concentration of at least, but not including,50% by weight of the biodegradable composition.
 10. An article ofmanufacture as defined in claim 1, wherein the stiff thermoplasticbiodegradable polymer has a glass transition temperature of at leastabout 15° C.
 11. An article of manufacture as defined in claim 1,wherein the stiff thermoplastic biodegradable polymer has a glasstransition temperature of at least about 25° C.
 12. An article ofmanufacture as defined in claim 1, wherein the stiff thermoplasticbiodegradable polymer has a glass transition temperature of at leastabout 35° C.
 13. An article of manufacture as defined in claim 1,wherein the soft thermoplastic biodegradable polymer is included in aconcentration up to about 70% by weight of the biodegradablecomposition.
 14. An article of manufacture as defined in claim 1,wherein the stiff thermoplastic biodegradable polymer is included in aconcentration up to, but not including, 50% by weight of thebiodegradable composition.
 15. An article of manufacture as defined inclaim 1, wherein the stiff thermoplastic biodegradable polymer isincluded in a concentration up to about 45% by weight of thebiodegradable composition.
 16. An article of manufacture as defined inclaim 1, wherein the soft thermoplastic biodegradable polymer has aglass transition temperature less than about −4° C.
 17. An article ofmanufacture as defined in claim 1, wherein the soft thermoplasticbiodegradable polymer has a glass transition temperature less than about−10° C.
 18. An article of manufacture as defined in claim 1, wherein thesoft thermoplastic biodegradable polymer has a glass transitiontemperature less than about −20° C.
 19. An article of manufacture asdefined in claim 1, wherein the soft thermoplastic biodegradable polymerhas a glass transition temperature less than about −30° C.
 20. Anarticle of manufacture as defined in claim 1, the biodegradablecomposition further comprising at least one particulate filler.
 21. Anarticle of manufacture as defined in claim 20, the particulate fillerbeing included in an amount so as to render the article of manufacturemicrowaveable.
 22. An article of manufacture as defined in claim 20, theparticulate filler being included in an amount of at least about 10% byweight of the biodegradable composition.
 23. An article of manufactureas defined in claim 20, the particulate filler being included in anamount of at least about 20% by weight of the biodegradable composition.24. An article of manufacture as defined in claim 20, the particulatefiller being included in an amount of at least about 30% by weight ofthe biodegradable composition.
 25. An article of manufacture as definedin claim 20, the particulate filler comprising at least one of silica,calcium carbonate, clay, talc, mica, alumina, or ceramic.
 26. An articleof manufacture as defined in claim 1, the biodegradable compositioncomprising a film or sheet that has been laminated to at least one sideof the fibrous sheet.
 27. An article of manufacture as defined in claim1, the fibrous sheet comprising tissue paper, paper or paperboard. 28.An article of manufacture as defined in claim 1, the fibrous sheetcomprising 8-60 lb/3000 ft² paper prior to being coated or impregnatedwith the biodegradable composition.
 29. An article of manufacture asdefined in claim 1, the fibrous sheet comprising 12-15 lb/3000 ft²tissue paper prior to being coated or impregnated with the biodegradablecomposition.
 30. An article of manufacture comprising: a fibrous sheet,at least a portion of the fibrous sheet being coated or impregnated witha biodegradable composition that renders the fibrous sheet moreresistant to liquids, the biodegradable composition comprising at leastone type of polyhydroxybutyrate.
 31. An article of manufacture asdefined in claim 30, the fibrous sheet comprising tissue paper, paper orpaperboard.
 32. An article of manufacture as defined in claim 30, thefibrous sheet comprising 12-15 lb/3000 ft² tissue paper.
 33. An articleof manufacture as defined in claim 30, the biodegradable compositioncomprising at least about 30% by weight of an inorganic filler.
 34. Anarticle of manufacture as defined in claim 33, the inorganic fillercomprising at least one of silica, sand, crushed rock, bauxite, granite,limestone, sandstone, glass beads, aerogel, xerogel, mica, clay,alumina, kaolin, microspheres, hollow glass spheres, porous ceramicspheres, gypsum, insoluble salts, calcium carbonate, magnesiumcarbonate, calcium aluminate, magnesium carbonate, titanium dioxide,talc, ceramic, zirconium compounds, xonotlite (a crystalline calciumsilicate gel), lightweight expanded clay, perlite, vermiculite, pumice,zeolites, minerals, or other geologic material.
 35. An article ofmanufacture comprising: a fibrous sheet, at least a portion of thefibrous sheet being coated or impregnated with a biodegradablecomposition that renders the fibrous sheet more resistant to liquids,the biodegradable composition comprising: at least biodegradablepolymer; and at least one inorganic filler included in a concentrationof at least about 30% by weight of the biodegradable composition.
 36. Anarticle of manufacture as defined in claim 35, wherein the biodegradablecomposition comprises at least one soft biodegradable polymer having aglass transition temperature less than about 0° C.
 37. An article ofmanufacture as defined in claim 36, wherein the biodegradablecomposition further comprises at least one stiff biodegradable polymerhaving a glass transition temperature of at least about 10° C.
 38. Anarticle of manufacture as defined in claim 36, wherein the biodegradablecomposition comprises silica as the inorganic filler.
 39. An article ofmanufacture as defined in claim 38, wherein the article of manufactureis microwaveable.
 40. An article of manufacture as defined in claim 35,the fibrous sheet comprising 12-15 lb/3000 ft² tissue paper.
 41. Amethod of rendering a fibrous sheet more resistant to liquids,comprising: providing a fibrous sheet; and coating or impregnating thefibrous sheet with a biodegradable composition in order to render thefibrous sheet more resistant to liquids, the thermoplastic biodegradablecomposition comprising: at least one soft thermoplastic biodegradablepolymer having a glass transition temperature less than about 0° C.; andat least one stiff thermoplastic biodegradable polymer having a glasstransition temperature of at least about 10° C.
 42. A method as definedin claim 41, the method comprising: heating the thermoplasticbiodegradable composition so as to form a thermoplastic melt comprisingan initially flowable composition; applying the thermoplastic melt to atleast one side of the fibrous sheet so as to coat or impregnate thefibrous sheet; and allowing the thermoplastic melt to harden.
 43. Amethod as defined in claim 42, wherein the thermoplastic melt is appliedto the at least one side of the fibrous sheet using a doctor blade or byspraying.
 44. A method as defined in claim 43, wherein the thermoplasticmelt has a melt flow index of at least about 40 g/10 min.
 45. A methodas defined in claim 43, wherein the thermoplastic melt has a melt flowindex of at least about 70 g/10 min.
 46. A method as defined in claim43, wherein the thermoplastic melt has a melt flow index of at leastabout 100 g/10 min.
 47. A method as defined in claim 41, the methodcomprising: heating the thermoplastic biodegradable composition so as toform a thermoplastic melt comprising an initially flowable composition;forming a sheet or film from the thermoplastic melt; and laminating thesheet or film to at least one side of the fibrous sheet.
 48. A method asdefined in claim 47, wherein the sheet or film is formed by at least oneof casting, extrusion or blowing.
 49. A method as defined in claim 48,wherein the sheet or film is laminated to the fibrous sheet byco-extrusion.
 50. An article of manufacture as defined in claim 41, thefibrous sheet comprising tissue paper, paper or paperboard.
 51. Anarticle of manufacture as defined in claim 50, the fibrous sheetcomprising 12-15 lb/3000 ft² tissue paper.